In order to use Grcpool to earn Gridcoin through BOINC project crunching, you will need to complete a few steps...

Register your Gridcoin wallet with the pool.
Access the registration page, fill in your GRC address from your wallet, and then "Submit GRC Address"
Verify GRC address ownership.
Next, you will need to "sign" the provided message in your GRC wallet to prove you are in control of the GRC address you provided.
Receive your password from Grcpool.
Next, you will receive a password from Grcpool which you will use login to the BOINC client Account Manager. Be sure to keep this password as it is not reproducable from the pool.
Setup Grcpool as a BOINC Account Manager.
Next, go to your BOINC Client, "Tools" menu, "Use Account Manager" item, select "GRCPool" and click "Next".
Login to Grcpool from BOINC.
Next, you will enter the GRC address you verified with the pool as well as the password which the pool provided in step 3, and click "Next". If successful, your BOINC Client will now be attached to the pool. There is also a new option "synchronize with grcpool.com" under "Tools" for when you make changes to your pool projects and want to immediately pull them into your client.