FIFA steep pass and flat pass?

When should you do a steep pass in Fifa and when should you do a flat pass? And what is the use of strengthening the passports or making them harder with RB and X or Y on the Xbox?

Flat pass if you play in the middle of the field steep pass if you play somewhere outside or behind in defense

With Y you just shoot the ball away

With X you should cross

And Rb I unfortunately do not have had a control myself