Log in with your username and password on the SIP portal
Click on the "Groups" tab in the tab menu
This will open the list of Groups on the SIP Portal. Search for the appropriate group you wish to join.
When you find the group you wish to join, click on the group's name to go to their Group Page
In the group page, note that an "Open" membership will have a "Join" link at the bottom of the Group name and description; clicking "Join" will automatically make you a member of that group.
Other groups will require you to request for a membership and clicking "Request for Membership" will bring you to a page where additional details can be filled out and to confirm membership by clicking "Join." Admittance to the group depends on the group manager's response.