Spanish slang questions?

I take Spanish in school, but I love it a lot and school is definitely not the reason I care about it. I want to become fluent in it someday, but right now I'm more like at an intermediate level. The Internet is super helpful, but some things like slang are so hard to find out! This isn't for homework, it's because I just really want to know.

How do you say "wait" in Spanish? I know the verb is esperar, but I don't mean like waiting in lin,e I mean like kind of slangish, "wait, what did you say?" kind of way. Would it be "Espera" anyway? Or do people not say this in Spanish?

How do you say "cool"? I have done so much research on this and I know it varies from country to country, but aren't there any universal words? I would say genial generally, but this can't be the only way.

Do people speaking Spanish have any word they say like "like" in English? Not gustar/querer, I mean like in the same way people do when they're talking quickly in English, where they say things like "I went to the store, like, for apples and, like, bananas". I have a huge problem with this in English I need to get rid of, but I'm sure if Spanish people do have a word like this it makes you sound a million times more fluent and like a native speaker.

Thank you so much! Sometimes learning Spanish feels like my life =D