Q: problems installing latest os x

I am having a problem installing OS X El Capitan. I had this same issue with the last OS X system but gave up trying to find a solution to it then. So, this time I am asking the community.

After I agree to the Software License Agreement I come to the screen where I select where to install the program. This is where I encounter my issue. The errors read "OS X cannot be installed on "Macintosh HD"." and "This disk is used for Time Machine backups."

I'm not the most computer literate person, but usually I can figure out what to do on my own - thank you search engines. In this case, I am at a complete loss. Any thoughts/suggestions?

Thanks!