It is very easy to solo mine with the official GUI. If you have not done so already, go to the <a href="{{site.baseurl}}/downloads/">Monero downloads page</a> and download the official GUI for your operating system. Then, run the setup and be patient as Monero synchronizes with the network. You should see that it displays "Connected" in the lower left corner.
You should now have an option to start mining. You can optionally change the number of threads to mine with. For optimal efficiency, you should mine with your CPU's cache divided by 2. You will need to look up your CPU's specs on the manufacturer's website. If you are unsure, leave the number of threads at 1. Click the "Start mining" button.