Unless you DO want to use if for commercial purposes, keep answering the questions that you NOT and it is for personal use only to get the FREE version.
When you have it installed, there are a number of places you can find help with using Sketchup, but I found Joe Zeh's site gives excellent tutorials. You might find that downloading the videos and looking at them off-line is worthwhile.
There are other SketchUp resources but my advice is that if your resource starts talking about Groups and not Components then walk away and get the item in my link.