Can I use my own layout and enter php tag?

Hi,

I just downloaded word press to try it out. I’ve been using news posting blogs for years, but the one I have now has a big security vulnerability, so I’m looking at upgrading.

My question is: I’m used to just inserting the php tag for the type of template and categories into my own template. I can’t seem to find anything like that here. Do I have to use word press’ layouts? Can I use my own and enter in the php tag like I’ve done with other posting programs?

Thanks!