Do i need to get it? will i be able to play online if i get forged alliance only?

Yep. Just be aware that the standard online client was recently closed.

If you want to play online, you'll have to use the community client (from HERE).

You only need Forged Alliance, and you now can only play online on steam, faforever.com or direct ip, and all options give all factions only with FA.

is there a guide for using those other clients? i've never done it before haha

www.faforever.com

There is a wiki, but it's straightforward (the client will guide you on every step).

FAF is really really fun
Thanks to pilot for making it while i was banned of faf

Once you installed FAF all you need to do is try to host and let faf patch your game to the latest and you can play online and have great fun

Back in the day, if you only bought FA, you only could pick to Sera to play online on GPG.

Now you can register a FA (or Vanilla) game key on Steam and get the "Gold Edition", which has both SupCom [Vanilla] and FA, to download and install.