It is easy! In the wallet go to help -> debug window -> console
and then type setgenerate true or setgenerate true 1 to use just one thread (Keep Your CPU partly free)
To check mining status the command is getmininginfo
1. Download the wallet (Mac or Windows).
2. Run wallet and click on help
3. Click on debug window
4. Click on console
5. Type on comnad line setgenerate true or setgenerate true 1 and enter (to use just one thread )
Now you you mining CAT and helping Catalonia!
6. To check mining status type getmininginfo and enter