When you decide to install contribution or module, or just change few things in your template, you might run into problem. Most likely this problem will be simple question: "How can I find my template files?". Though, answer to this question is as easy as question is.
To discover location of your template:
1) Navigate browser to URL of your store.
2) View HTML source of store main page (in IE: Right click on empty place -> View Source).
3) At the top of file locate line that looks like <link href="templates/XXXXXX/stylesheet.css" rel="stylesheet" type="text/css" >
4) XXXXXX is your template folder name. You can find template files by accessing templates/XXXXXX/ directory using your FTP client.