hey this is my first guide ever but i tried my best , i choosed jax cause he is one of my best champs, i will try to explain some things here and pls leave a feedback for me .

i take these runes cause they give you everything : armor, magic resist,dmg and sustain it makes the early game easier and is still enough for the late game

i tool 21/9/0 because as jax you want to maximize your damage but you still wants to be a little tanky too,

i showed 2 possible builds but i go for the first one normally cause you are more tanky with it as with the second but the second is actually pretty good too if you have to deal more damage

i max the Q first because it deals the higehst damage with your ad items but i max the W second because of the low cooldown which procs your trinity force faster.

ignite and flash are the best spells for jax because it gives you mobility and outrade potencial but you could take cleanse with you instead of ignite if the enemy has very high cc this is a advice for the draft pick mode

Pros:

Very good 1V1 fighter
has a stun
can dodge autoattacks with his E
has an Escape
destroys carrys in teamfights if you catch them offguard
Aoe stun
good engage

Cons:

low range Aoe damage
if you get focused out you cant do very much
no real teamfight strength untill you can get someone offguard
if you engage in the wrong time you are popably dead because you wasted your escape then

jax works good with champs who have high cc because his autoattacks are the main point on jax so champs like Leona or Nami are really good with jax in team

jax is a really strong 1v1 fighter and can outrade most of the champs and has a really high potencial to kill , he is the only champ who can dodge autoattacks so use that to take advantage of champs who need their autoattacks like Yi,Fiora,aatrox,irelia and every AD carry and his ult has a passive who deals extra magic dmg on every third autoattack

just farm with your autoattacks in early game and in mid to late game you can use your passive from your ult to last hit better

jax has a very high potencial to carry games if you get many kills you can outtrade almost every champion in 1v1 situations in mid and late game . so i hope my guide helped you to improve your play with jax , as i said its my first guide so pls leave a feedback