From the Forum User Guide:

What are the different Ranks, and how to earn them?

Rank 1 - New/Inactive
This is the rank everyone starts with. You don't have access to some sections of the board, or the PM (private messages) system. You need to interact here a little first for us to be sure that you are a Transformers fan, and we will activate your full Basic membership.

Rank 3 - Basic Member
When someone has interacted here a little, or posted an introduction, it helps us see that they aren't a spammer/scammer, and they gain this ranking, which gains access to the Meets and Sales sections, plus the PM system.

Rank 5 - Dedicated Member
Upgraded Basic Members after a few hundred posts or significant contributions to the sightings, news and info sections. It increases PM mailbox quota and possibly some preferential treatment with events or promotions that have limited availability.

Rank 6 - Deluxe Member
Only offered to dedicated fans who can be verified that they are over the age of 18, for continually contributing to the community as a fan. They are rewarded with a greater PM mailbox quota, Ozformers exclusives, and priority access to other exclusive or limited things... but it is also a position of responsibility, as they are expected to represent the standards of this site and community.
Basically, continue to be involved.

As a Basic Member, you've got access to pretty much everything the board has to offer - sightings, discussions, sales threads, etc.

The bonus of extra storage space (and therefore burden on the board's servers) coming as you establish yourself more and get involved with the various aspects of the community.

Welcome to the boards! We hope you've been enjoying yourself so far, and look forward to sharing in our hobby with you, whether you want to show off you collection, discuss comics, or provide your thoughts on different figures, we cater to almost all tastes here.