[themes] tpl.php file question

[barb]

> As far as I know drupal only passes the node object to node-tpl.
> You will have to process other non-related variables before trying to use
> them in your tpl file.

mhm - i thought so already, but wasnt't sure. so if i see this right,
i have to preprocess the variables in the template.php in order to make
new variables available for the node script?

i am doing this for the first time and have hardly any experience in php
 - so i am really puzzled about making new variables available thru
template.php. any help would be appreciated or a link to a good manual?
(or do i have to learn php from scratch ;)
i've checked out quite some manuals but i don't really understand the
processing....
thx
b#