I just checked my website in Google and I noticed that Google had indexed my homepage as 2 different files. One is the main web address and the other is followed by /index.html. Is this considered repeat content and if it is, how do I fix this with a 301 redirect?
You'll want to read about canonicalization. Matt Cutts Blog is a good place to start. He has addressed this issue many times. http://www.mattcutts.com/blog/seo-advice-url-canonicalization/ Google has even created a TAG to address this issue.
Yes its different, you are sharing your link juice to two websites, while one is obsolete. Use 301 redirect from .html page to main domain and also use "/" on the end because without it on some hosts domain can be considered as another different page and dont forget that while link building.
Thanks guys! I believe this is a problem that was effecting the SEO of some of my websites in the past. I just fixed it.