To be good at something; to be able to do something well. Also used colloquially to say something will go well.
彼はギターがいけるから、バンドに誘った。
He's good at guitar, so we invited him to the band.
準備は十分だし、試験はいけると思うよ。
We've prepared enough; I think the exam will go well.
この仕事、君ならいけるよ。自信を持って。
You can handle this job. Be confident.
To look/sound/taste good; colloquially used to mean 'it's good,' 'tastes good,' or 'looks attractive.'
このレストランのパスタ、けっこういけるよ。
The pasta at this restaurant is actually pretty good.
その服、いけるね。似合ってるよ。
That outfit works — it suits you.
この企画、見たところいけると思う。
At a glance, this plan looks workable.
To be able to hold one's liquor; to be good at drinking alcohol (can drink a lot without getting drunk easily).
彼は酒がいけるから、飲み会では頼りになる。
He's a strong drinker, so he's dependable at drinking parties.
私も今日は調子がいいから、いけるかもしれない。
I'm feeling good today, so I might be able to keep up (drink more).
お酒がいけない人は無理しないでね。
If you're not good with alcohol, don't push yourself.