Your Rebel XS in an EOS camera, therefore it is compatible with any Canon EF or EF-S lens. It will also be compatible with '3rd party' lenses (Sigma, Tamron etc) as long as those lenses specify that they are for Canon EF, EOS, Autofocus etc.
There aren't really any tricks to using different brand lenses...they all basically work the same way. Although there are some differences, for example, a Sigma lens might zoom out by twisting the barrel in the opposite direction that you would for a Canon zoom lens.