How do I insert a custom rollover button within a page?

What I’m trying to do is place a custom “call to action” button at the top of my homepage. I have created the image sprite, the html index file & css stylesheet which are all located within a single folder. What I need to know is where exactly do I place the folder within my sites directory? How do I call the code once it is in place? And how do set it up to sit in the correct position on the page? ( I need it floating over another image on the top portion of the page just under the header)
I have been scouring the web for 3 days now trying to find a tutorial or something that might give me the answer to no avail and feel I have exhausted my search options. This is more than likely a simple fix for someone with coding knowledge but I am a complete newbie to this type of thing so you might have to dumb the solution down somewhat. Thanks a million in advance, I look forward to a solution to my dilemma. Cheers;)