hey man lol kindai dunno how to explain
regular squat is well u know it
then front squat pretty much the same but the bar is across your clavicles
zercher is ok imagine standing just behind a barbell. it has to be about your elbow height. then walk up to it, and wrapp your arms around and under the bar so its as if you're "hugging" it in a way, then stand up, and holding the bar like across your abdomen within your arms, then squat
just for something different
i found a pic for you mate check out just below half way the page
http://www.abcbodybuilding.com/magazine03/homegym.htm