Suck的用法
X sucks = X is very bad or unfortunate.
-That restaurant sucks. I never go there.
-That really sucks. I'm so sorry that happened.
-This place sucks. Let's go home.
Someone sucks at something. = They are very bad at it.
-I suck at snowboarding.
-She sucks at cooking.
-David sucks at math.
Suck is a verb, not an adjective.
That sucks. ✅
That's suck. ❎
However, we occasionally use the adjective "sucky", but usually we only use this to describe a situation.
-That's really sucky. I'm sorry you had to experience that.
Also, this is slang, and some people consider it rude.
I don't consider the word rude, but if you tell someone that they suck at something, that is definitely rude.