Judging from brevity of your post, you need to read the manual that should have come with FL Studio.
If,
for some way out and totally unexpected reason, you don't have the manual, try and find the documentation for it on the internet.
You need to read that and get totally acquainted with exactly how FL Studio works before you start looking at making music. Also some googling wouldn't go astray.
As far as free VST's go, do some forum trolling (here I mean troll through the forum - go back through the threads, there a a bunch with VSTs on them, like
this one - don't actually troll, because we don't like that here).
The one key thing that you need to remember is that you get what you pay for. If you want free VSTs you're gonna have a hard time making sounds like the pros do.
This does not mean you can't make good music.Also making a song using the default stuff in FL might be worth a shot just so you get to know how it works.
That said, welcome to MLR and enjoy your stay!
Disclaimer: I'm not actually someone who uses anything like FL studio - but I'm fairly sure most of this is universal for music