Click on a pool to learn more about the pool. After clicking on a pool, you'll be redirected to the Pool Info page.
Pool Info page
Click on the 'Deposit' button to open the modal. You should see something like this:
Pool Deposit modal
First enter the amount of mcUSD that you'd like to invest in the pool. Next, click the 'Approve' button to allow the pool contract to spend your mcUSD. Once the mcUSD amount is approved, click the 'Deposit' button to deposit mcUSD into the pool.
Once the transaction is confirmed, the 'Your Investment' section of the Pool Info page will be updated to show the USD value you deposited as well as the pool tokens you received.