Click on the earn tab as below:
On the top of Earn & Invest swipe the tob bar left until you find liquidity pool you would like to invest in. Your choice being XLM/CANNACOIN or USDC/CANNACOIN. Tap the arrow to enter the liquidity pool, as in the images below:
Here you can deposit and withdraw your liquidity from the pool. Tap Deposit, as in the image below:
You will need an equal dollar value of both coins in the pair. Type in the amount of CANNACOIN you want to add to the pool and the amount of the other coin in the pair will automatically be filled in.
Ensure that you have enough of both coins in the pair as well as XLM to cover the fees of joining the pool.
Then click Deposit. See the images below:
Refer to the video demonstration below: