Online tutorials for form validation in PHP

Greetings, I'm a beginner in PHP, so forgive me if I ask really basic questions! I've created a form that inserts data into a database, and so far, the form works. However, I don't have form validation included into this form, so I was wondering if someone can point me to an online tutorial on how to do this with an existing form. I've tried adding a javascript onclick form validation but the php code I programmed doesnt' take the javascript onclick into consideration. The php I coded takes the first three required field into consideration and if it doesn't have the values, it goes right back to the original form - but it doesnt' tell you what you did wrong - not very user friendly. -- Laurie Landry lmlweb@mybc.com - email (604) 693-1120 - voicemail/fax