What does “geekin’” mean?

Geekin‘, in drug culture, means hopped up on meth but, nowadays, you can use it pretty much interchangeably for being high on any drug. See also tweeking.

Why would you try to learn English using a song like this?

Geekin means on drugs, uppers in particular. A similar phrase is "geeked out" "Did you see that guy over there? He's geeked out" As others have mentioned it is slang

It means he is under the influence.

It's the meaningless chatter between two idiots.

Honestly, I have no idea. It's probably some slang specific to American rappers

It means "going wild, in an excited way", possibly/sometimes due to drugs. It's AAVE (and ALSO slang), and probably a little bit dated.

Viral means relating to a virus, but in the internet/fame/celebrity context “going viral” it means spreading rapidly. Hella is being used to mean “very”

Is this even English though?

Using a ton of drugs.

Are you trying to learn English through these lyrics?? wtf 

Other people have explained it, but I'd also add that most of the time I've seen it used, it didn't really imply drugs. It really just meant being very happy or excited. It can mean that, depending on context, like when this song was made for example. To "go viral" means to become very popular in a short amount of time. You'll see this be used with people, videos, memes, etc.

Others have already explained geekin' so here's 'hella viral:' Viral (adjective) = Something that spreads far and fast, like a virus. It's often used to talk about things that suddenly become extremely popular on the internet. For example, the video of the man dancing to the Numa Numa song is a viral video. The phrase 'to go viral' means to become viral. Hella (adjective/adverb) = Slang for both 'very' and 'a lot of.' In English, you can't say 'a lot of good' or 'I've got very money.' You'd have to say, 'very good' and 'a lot of money.' You can use hella for both of these though, something can be 'hella good' and you can 'have hella money.' Put those together and we get 'I'm going hella viral' 'I'm spreading very far and becoming extremely popular very quickly.'

Hella viral means very viral, hella is a lesser-common used slang word

Geeking means (in modern North American slang) means being jittery or overly twitchy because of hard drugs like amphetamines

I have no idea what any of this means. I would not consider this to be comprehensible English.

Um. I don’t think you want me to tell you what it means.

I use this word to just describe laughing with friends about something. “We were geeking about this moment back in college” If I’m with my friends at a club, and a girl calls asking to fuck…and I just say “Nah, fuck you, bitch” and hung up…we would all start laughing hysterically. Heavily induced by alcohol since they’re in a club. I don’t think you have to be high or under the influence to make this word apply, but it definitely involves laughing.