Welcome TomandDiego!
A good explanation of tiers can be found here: http://www.wgt.com/forums/t/108931.aspx
You should also understand "levels" because the higher your "level", the better the equipment that you are allowed to buy at the Pro Shop. See the last post on this page:
http://www.wgt.com/forums/p/48159/846092.aspx#846092
You will need "credits" to buy better equipment and you can either buy them or take surveys and do other 'activities' to get them free.
Trust me - FREE is the way to go and you should start gathering credits now, because you will want better gear pretty soon!
Enjoy this, it is both challenging and fun.