First of all, you need to update the GUI Chia. To do so, go over to www.chia.net, download and install the latest version of Chia. Then simply close your program, download the new version and run the installer. Wait for the program to start.
To activate a smart contract with a pool, you need to have a little XCH on our wallet. If you already got some, go ahead and skip this step. If not, click on the "Pool" section.
After clicking on "Join a Pool" button in case if you don't have any coins, you will be transferred to the faucet.chia.net, where you need to add you wallet address. If you having trouble finding the address, it's located on the "Wallet" tab on your menu bar of GUI Chia. Copy this address and paste it to the faucet.chia.net. Now just wait till your balance is filled up with some coins. This can sometimes take up to a day. If you are really not into waiting, you can ask someone from your pool to help you out here a bit by sending a mojo.