Custom Pages using forms: Problem

Hi, I was recently testing custom pages with forms and the form action doesn’t seem to work properly mainly because the parameters are (ex. mydomain.com/mypage) They do not include a .php in the ending, so the form doesn’t transfer the information. I was wondering how this could be fixed or the codes required to make a .php file able to communicate with the wordpress global variables such as logged in user, or even plugin variables.

Thank you.