Set camera to specify x,y in pixels? 2d

I am having trouble setting up the camera. I been learning unity and pretty much figured out what i needed however i have a problem specifying a few things.

First i wanted my screen to be 0,0 from the top and have a width/height of my choosing. I choose 800x600 to test with. Next i made cubes scale 10,10,1 (i accidentally had the right cube rotated). Then i figured out how to position the cubes and that wasnt an issue. Now my problems are

1. The cubes are actually 19x19 instead of 10x10
2. The center is 0,0. I thought the topleft would be since i made it 0,0,w,h
3. When moving the cube to the top left the position coords were -250x95. I dont know what it means but i know 250 isnt half of 800

How do i fix the camera so the top left is 0,0 and fix it so the size of cubes are 10x10 or w/e width or height i want in pixels