First open your wallet, and make sure you are connected to another wallet.
You are connected if you see the icon Wallet Connections in the lower right corner of your wallet.

The message "No block source available" will disappear once you mine your first block.

Please follow the FAQ instructions under My coin is out of sync if you don't see this icon.

Go to Help.
Click Debug Window.
This is the console where you will execute all commands.

Type this command to start mining your first block:

setgenerate true -1
If you want to use a specific number of CPU cores, instead of -1, type the number of cores.

You can then type the following to see the status of generation.

getmininginfo
It will take about +/- 10 minutes to mine your first block, depending on your computer hardware.

Open your wallet, and make sure you are connected to another wallet.
You are connected if you see the icon Wallet Connections in the lower right corner of your wallet.

The message "No block source available" will disappear once you mine your first block.

Close your wallet and create the file Yourcoin.conf in the folder "%APPDATA%\Yourcoin\". (replace "Yourcoin" with the name of your coin)

Paste the following text into yourcoin.conf and save the file.

rpcuser=rpc_user
rpcpassword=cca332523222d3e1e3d15744f
rpcallowip=127.0.0.1
rpcport=4210
listen=1
server=1
addnode=node.walletbuilders.com
Download the latest version of cpuminer from here and extract the zip file.

Create a .bat file named mine.bat and paste the following text into mine.bat.

minerd --url=http://127.0.0.1:4210 --userpass=rpc_user:cca332523222d3e1e3d15744f
Save the file inside the extracted cpuminer folder.

Open your wallet and execute mine.bat to start mining your first coins.