This guide is for all twitch newbies and lovers.
so for starters, I'm no pro I have been playing league since season 3 and quickly fell in love with twitch. And I want to share this to help anyone in seek of help while trying to learn this champ.
So along with this guide, I'll try to implement links to videos as we go through this for mechanics such as kiting basics and high attack speed kiting in the spaceglider style of ratirl and I'm taking him as an example just because he is the most well known high elo twitch main.
May you enjoy your cruise along the rat train. :))))

So for those that already know the champ this part is just a recap of his abilities and how they scale so if you're not interested or already know it all you can skip ahead.

Twitch's passive is a poison that is applied by his autos and by his W (more on that later) deals true damages scales with a 2.5%AP (15% at max stacks) Ratio and does 1 tick every second for 6 seconds and can stack up to 6 times and the 6s duration resets on every application.
//Good to know: if you have a cassiopeia on your team her E passive is triggered by this since it counts as a poison

Twitch's Q is an invisibility that lasts up to 10/11/12/13/14 seconds depending on the level of the ability. During stealth you gain 10% movement speed increased to 30% when moving toward enemy champions within a 1000 unit range (only if they can't see you though). Upon exiting the stealth you gain 40/45/50/55/60% attack speed for 5 seconds depending on the level of the ability.
//Good to know: This can be a good source of engage as well as a very good escape and its cooldown resets on takedowns

His W is a projectile that upon landing create a circle that slows your enemies and applies a stack of passive per second and lasting 3s and can apply up to 4 stacks of passive since it applies one upon landing too, the slow is 30/35/40/45/50% + 6%/100AP
//Good to know: Pretty obvious but while traveling to its destination your W is a projectile and thus can be blocked by abilities such as yasuo's windwall.

The E is the main source of damage on the AP build, it deals 20/30/40/50/60 base damage plus 15/20/25/30/35 + 35%AD and 33%AP in physical Damages to all enemies afflicted by your passive Within a 1200 unit range of you
//Good to know: If you cast it while an enemy is dashing out of range they will still be hit since it only counts the position they were at when the ability was casted.

Twitch's R Augments twitch attack range to 1100 and act kind of like a Xerath Q by modifying his autos into a target piercing with added width for 6 seconds and adding 30/45/60 physical damage on hit and these can critical strike and apply on hit effects such has runaan and Botrk.
//Good to know: while under the effect of R you outrange towers of 50 units.

Since twitch is a squishy champion as are most of the adcs your goal is to deal damage from afar so one of the main things you must know is how to place yourself in lane and in teamfights to not be too vulnerable.
For this I'll recommend watching this video for teamfights and skirmishes https://www.youtube.com/watch?v=ij7iPqKDwv0
and for the lane I think this one will fit perfectly
https://www.youtube.com/watch?v=a3c7BVq5WYY

To help that I know it's gonna sound obvious but communication with your team will be necessary

Twitch has a very peculiar playstyle even for an adc since he must be played kind of like an evelynn when invisible take advantage of the fact that enemies cannot see you to place yourself well for a fight if you wanna engage one else just pressuring them by playing relatively aggressively then going into stealth so that they think your jungler might be on his way or that you are ready to engage a fight. The best example I can take for that is when you're at one cs from level 6 and if you have priority you can go invisible and get 6 then jump on them out of nowhere it'll guarantee you at least one kill if you placed yourself well and your support follows your engage.

same goes for roaming, as twitch roaming can allow you to scale faster and help your other lanes (mainly mid, but also your jungle by being there on objectives)

Twitch does not have a strong early so you're better off scaling by farming his first spike on ad is boots + mythic whereas on ap just blasting wand + berserker boots will help you have unexpected burst damage from a twitch this early in the game.

Another strong point of twitch is since he can be played ap or ad you can adapt to your team's needs.

For this chapter I will only link videos for different level of kiting since it would be impossible to explain it with words

Basics explained and settings
https://youtu.be/m4sCpRo07aQ

More advanced techniques and tricks
https://www.youtube.com/watch?v=FWJufSUDW28

and for those of you that don't know what pro kiting looks like here's a little montage of Ratirl
https://www.youtube.com/watch?v=_vlD31NMEms

Basically for your settings in-game:
Use Player Attack Move Click
Attack move on cursor
Disable movement prediction

Well this isn't a chapter where I say if you wanna climb duoQ is your best option but I honestly advise you to try it with a support main if possible or a jgl main. if your duo is your sup then great communication will surely be easier (being able to be on discord is awesome) since they will most likely be playing an enchanter support and you can truly cooperate the best with someone that will hear your calls at the instant you're gonna make them and you can also not be enduring the ranked system alone.

Also even though it's not on duoQ downloading replays of the games and watching your mistakes is a great way to learn (through trial and error is the best way to learn) also watching your stats on porofessor is a great idea and the other thing you can do is simply watching high elo streamers play on adc and especially on twitch for the matter of this guide but it works on almost any champ. It helps you understand the core mechanics of the champ, that is only if you have already the mechanical mastery of league.

Twitch has a lot of bad matchups, but like all the champs and even if you're falling behind you must learn to adapt to your build accordingly to the enemies like if the enemy botlane is a double mage bot then before even thinking of mythic try to go for wit's end if you're ad if you're AP the bot matchups aren't as hard as they are on AD since you can just poke from far away and land hard punishes on any mistake you can see.
So for adaptability I recommend you watch the notes I put on the builds I tried to make them as clear as possible if anything isn't clear leave a message on this guide's discussion page even if I'm not the one responding then someone else might have understood it and will help you but I will try to give my best advice and answer any question on this guide.

To be honest I made this guide because I spot a lot of people playing twitch not knowing what to build or which runes to take to exploit the best out of this champ's potential and I am truly grateful for you reading it this far.

So now all you gotta do is train in the practice tool and play normals with Twitch until you feel ready to be playing it in ranked or even just to show off to your friends.

Thanks for following this guide I will update it as time goes on if I see anything that I might have missed.