Have you gone to the front page of the group and clicked the button to join, most clubs you have to request to join, then wait a few days.
When you have a request in, it will appear in your message as either submitted (which means they have not approved or declined) approved or declined. Once it is approved you can begin to submit art.
I don't belong to any groups that require point donations, but they certianly could exist. All the groups I belong to are free for people to join, and I generally join those that are not for a certian skill level but open to all. Read the group guidlines prior to trying to join.