The link to Deposits and Credits doesn't tell you very much about earning credits through surveys, etc.
Mousing on "Get Credits" at the top of the page gives you two choices, buying or earning. Click "earn free credits" and from there browse through the successive pages. Survey sites can be found in several locations. Doing Surveys will get you a fair chunk of credits quickly IF there are any surveys on offer at that time, and IF (really big IF) the companies come through with the points. Often they will collect a bunch of information and then tell you you're not the type of person they want to collect information from. You can believe that if you wish.
There seem to be a lot more surveys available at the beginning of the month; far fewer later on. Be patient. Sometimes you might get 400 or 500 points in a single day. Other times you might wait two weeks and get 10 or 15. (personal experience; apparently there are different surveys in different countries. No surveys at all in some others)
Watching videos is terminally boring but it gets you seven points a day and if you go back every day, once you have watched 100 videos, you can redeem them for 75 points. Not enough to keep you in balls unless you are a very accurate hitter and prefer cheap balls, but it all helps.
Following through the other offers is also a hit or miss proposition. Known and trusted companies are a fairly good bet, but the ones that offer thousands of points for your credit card number probably aren't out to become your best friend. Beware. It's not just WGT trying to make money on this site.
Earning credits by playing tournaments is a viable proposition only for the very very good players, except for the CTTH tournaments which have a draw for credits, in which case the odds in your favor are very very slim.
At the end of the day, you can have a lot of fun playing the game without expending too many credits. Half the fun is chatting to the golfers you're playing with. A few are complete lost causes, but the majority are great people.