Gravity? Collision Platformer.

Thanks everyone, sorry for the late replies(real life..)

I've been trying to figure out the collision between my two rectangle. I don't quite understand it yet with what you guys provided me. As for increasing gravity, well gonna add it after I can actually touch the ground and move right and left lol(same goes for jumping).

So let's start with my collision...
I'm not quite sure why my piece of code won't let me modify gravity..?

SuperStrict

Graphics 800,600,0

'********************************************************************************************
Global GameRoom:Int		=0
Global GameExit:Int		=False

ResetCollisions()

Local P1:TPlayer=New TPlayer; P1.Create(10.0 ,10.0 )
While Not GameExit=True
	If(KeyHit(KEY_ESCAPE))Or(AppTerminate())Then GameExit=True
	
	P1.Updates()
	MakeSolid(0,560,800,25)
	Flip 1
	Cls
Wend
End

Type TPlayer
	Field health:Int, mana:Int
	Field xpos:Float, ypos:Float
	Field maskw:Int=70, maskh:Int=120
	Field gravity:Float=1.0
	Field jump:Int=False
	Method Create( xstart:Float, ystart:Float )
		xpos=xstart
		ypos=ystart
	End Method
	Method Updates()
		If KeyDown(KEY_UP) 		Then ypos :- 5.0
		If KeyDown(KEY_DOWN) 	Then ypos :+ 5.0
		If KeyDown(KEY_LEFT) 	Then xpos :- 5.0
		If KeyDown(KEY_RIGHT) 	Then xpos :+ 5.0
		If KeyHit(KEY_SPACE)	Then jump = True
		
		ypos :+ gravity
		
		Self.Drawing()
		
	End Method
	Method Drawing()
		DrawRect xpos,ypos,maskw,maskh
		CollideRect xpos,ypos,maskw,maskh,0,1
	End Method
End Type

Function MakeSolid( x:Int, y:Int, w:Int, h:Int )
	DrawRect(x,y,w,h)
	If(CollideRect(x,y,w,h,1,0))Then
		P1.gravity=0
	EndIf
End Function

Not Quite sure how to design my level should I make a function which draws all the masked SOLID background that would collide with my player's rectangle mask?

*shake his head and goes take an advil* xD