Irelia is a difficult champ to master but there aren't hard mecanics to learn as long as you reset the Qs and stack the passive because the passive gives you a tons of magical damage plus attack speed based on your level so Irelia is a very scary champ with the full passive active

The main combo for Irelia is the 3Q
first you set the E1 down the R and Q at the same time then E2 and Q and Q
try to AA (auto attack) in the middle of the ability

E1 > R > Q > E2 > Q > Q
the perfect combo will be:
E1 > AA > R > Q > AA > E2 > AA > Q > AA > Q

E1 is the first cast of the E
E2 is the second cast of the E
R is the Ultimate
Q is the Q
AA are the auto attacks

Irelia is a hard champion to master but there are some tips I can give.
at level 4 with 2 points with the Q you can oneshot the melee and caster minion with a full charged W
at level 7 you can oneshot the minions with half cherged W
at level 9 you can tap the W and oneshot the minions
at level 10 you can oneshot caster minion with only the Q.

Another Tip:
You can W on top of the E1 and wait for the incomint CC then E2 to react and stun the enemty.
First place E1 and than hold the W on top of the E1 then wait for the best moment to E2 and stun the enemy

Another Tip (TeamFighs):
Wait for the best momento to go in and kill the enemy.
if you go in and take all the CC you will die, place the R and wait for the CC then go in try to go to the low health champs or ADC and Support (if it have low health or is not a tank nor have can heal itself)

Don't worry if you suck at first, you will get better in the adventure to be good with Irelia. I hope you find this guide helpful and I hope that you will as strong as you wish to be. Have fun playing Irelia