Step 1: Open Google Mail and open the settings:
Step 2: Switch to the accounts tab:
Step 3: Click the link to "Add another email address" underneath the "Send email as" section:
Step 4: In the new window, enter the email that you would like to send as. You can use any of the email addresses that you have at OSU. A few examples include Evan.Brass@oregonstate.edu, email@example.com, Scholastic.Arts@oregonstate.edu, etc. Be sure to uncheck treat as alias, unless you know that you check the email addresses seperately and you are sure you want to see those emails in the account you're logged into. This is a rare case.
Step 5: The confirmation process can change, in some cases you may be asked to setup a connection to campus mail servers but in most cases you'll be asked if you want to have a confirmation code send to that address to confirm that you control it. Click "Send verification":
Step 6: Enter the verification number you receive in the address you would like to send as:
Step 7: To send an email as that account, start creating the email and then click on the from address to switch to your new account: