Difference B/W

hi.......every one

i am new to ios

when i run simple SingleView Application in my i am facing lot of problems with Retina selection

chages buttons, labels postions on simulator

is there any difference between Retina3.5 ,Retina 4.5 ,Freeform , None.

which is i prefered above 4 types .

& Explain or give any usefull link also

Thanks Inadvance to Every One:)