[Plugin: List category posts] styling

I’m afraid this will sounds like a very stupid questions – I’m brand new to all of this, only strated trying to put a website together a week ago.

But anyway, I’ve found this plug-in very useful. So I went a crated several templates, but now realise that I have no clue how to link them to my css file or where to insert css styling. I’ve read all the instrusctions on the website many times, but I just don’t know enough to understand them fully. If someone could just give ma an example of how, for example, I could change the size of the fonts of the post titles I list on the page, I would be very grateful.
Thank you!!!

http://wordpress.org/extend/plugins/list-category-posts/