template

Sorry, I'm sure this has been asked before but I couldn't find anything on the forum....
Will a template that I install on my joomla 2.5 website work with opencart? Or do you need to install a seperate one for opencart? How do they work together so it looks like opencart is part of my website?

Joomla and Opencart are two different systems, they can't use the same template. If you want to make them look alike, you'll have to modify or create the opencart theme to look like your joomla website.
They don't work together but there's some extensions for Joomla that integrates both together:
http://extensions.joomla.org/search?q=opencart
They're all commercial, and I actually never tried any but I have seen good feedback from it.

Good luck!