Secure forms using php sessions with tokens

[johnboy]

Hi Alex,

I am new to php and would like to see a video tutorial on securing forms using php sessions with tokens.
I was following another channel on youtube (phpclass) and found a screencast on "Securing forms using tokens". I get the general idea that the form is digitally "signed" and stored in the token and then subsequently checked. What phpclass does'nt explain is how a hacker would intercept a form and does using tokens completely secure the form? Perhaps you could explain this very important subject of php security.

Thanks.

PS. I think your php screencasts are one of the best on the web.