changing frontend look - what *.php to change?

[Eskimodesign]

Hello,

first, sorry for my worse english, i hope its possible understand me and my problem.

I need to re-design the layout of the formular-area which is seen in frontend bascially.
Where i can find the *.php to change custom the look of my formular (css doesnt give me enough for make my wished-changes come true).

thx in advance

Kind regards
Reiner