Levels come with eXperience Points (XPs), and these are WGT's Brownie points for diligent play on this site. Levels release equipment to improve the playing experience (and the company's revenue). Some explanation in the FAQ ==>
Here's the Level&XP reference.
You can sell clubs back to WGT at a 25% rate, but not those provided for free.
About upgrades:
IMHO the most valuable first buy would be two short wedges, Ping brand or higher.
Low level buys tend to become pointless too soon. Whatever you want to buy,
look out for the possible better equipment available at a higher level. In
general, unless the need for a change is irresistible,
- do not start to buy wedges before level 18,
- do not start to buy a putter before level 30,
- do not buy a putter below 500 credits,
- do not start to buy woods and irons before level 32,
- start buying balls as a Tour Pro, work your way through the list from
cheap to expensive. Try to avoid using a ball with higher level than your
main clubs.
May I conclude that one possible effective(!) sequence of clubs may be seen
in a selection of
L32 R11 - L59 G20 - L79 Bladez (L83 G20) - L90 R11
(XPs: 12,900, 88,500, 200,000 (255,000), 487,000)