I found an old laptop and waited for it to sync, and I set mining to "solo mining on".
How do I know if it's mining in the background? Also, sorry for all the questions but I have one more :-)
How do I find my HODL address?
Thank you for all the help!
Depending on how old a laptop it is...you'll know you're mining when smoke starts to raise from the innards.

In all seriousness though, if your CPU usage is at (or near) 100% for the wallet process, you're mining.
Find your HOdl address by choosing 'File > Receiving Addresses' from the menu (just like in the BTC wallet)...assuming you're using the Qt GUI wallet.