Problems editing home page

Hi there,

I’m a bit of a novice with, well everything really. I’m trying to add some codes to my home page (just an extra button) which I think I have to use wp editor for (rather than any individual page).

However when using editor there isn’t a preview option and I’m terrified of messing with the rest of the code (which someone else has put together and looks great). Is there a way to preview any changes I make before saving them?

I’ve tried looking for plug ins but couldn’t find anything I was sure of, and I also tried Dreamweaver but it wouldn’t display anything correctly and just got more confusing with each new tutorial on the subject). Any help here would be really appreciated, thank you