DSLR camera is digital version of slr film camera .
full form is single lens reflex ,
well in lame term , what you see at view finder so you get in the picture ,
both viewfinder and sensor of camera get the the light though one lens .
well most notable difference of dslr or slr is that they offer changeable lens and offer many modes to shoot , you can control shutter , aperture and other things in the camera .
well , t2i ?? well why do not you consider getting consider nikon d3100 , you do not need anything more than that , that's perfectly adequate for all your need.
look at this picture go gauge how does dslr/slr work
http://upload.wikimedia.org/wikipedia/commons/a/a0/SLR_cross_section.svg