Dude,
If you are going to run a seminar you gotta be a guru or something...
Since you don't know much about php, firstly go ahead and get some experience writing code, debugging code... etc... and then run your seminar.
As far as your question concerns...
1. Go to www.yahoo.com scroll down untill you see computers and internet category. Click on that and within this directory search on php - that should get you started.
- Go to php.net and read their manual. A lot of functions that they describe also has a good user input.
Hope that helps,
Di