How to use github generally as a dev and a consumer?

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Hi, This is a general question about how github can be used as a developer and as a user. I see interesting things on there, like the link below, but I am not sure how I can consume the code for myself, as in installing in in Mac OS X (there is no mention of operating system in the example below).

I would also like to, as a developer, use Github if someone can share why I should care about it as a developer:)

Also what is Git?

Google says:

git
/ɡit/
nounDEROGATORY•INFORMAL
an unpleasant or contemptible person.
"that mean old git"

but I doubt this is the intended meaning in the context of software dev.

Thanks in advance y'all. Now I said git!

What I have tried:

GitHub - iamadamdev/bypass-paywalls-chrome: Bypass Paywalls web browser extension for Chrome and Firefox.[^][^]