Can you suggest any good reference on path analysis please?

This is not basically a research question rather an ask for help to provide me with some useful references on Path Analysis. This seems to be a trendy technique, but looks a little bit complicated. Is there any downloadable complete free book or PDF where I can find details on its theory and usage?

I need to learn the technique for mixed type of variables. Which is the easiest software for performing path analysis? I have heard about AMOS. Can't we do it in SPSS? I would also like to have suggested some references where I can learn how to use the referred software for path analysis with mixed types of variables.