As a member of our Plus membership service, users receive a set number of credits per month which they can use towards product downloads (20-50 depending on the plan).
Plus credits can only be spent in the Plus Hub - they cannot be used on regular marketplace purchases or $1 Deals -- however, there are some bundles which will allow you to use Plus credits.
Plus credits can also be earned by participating on the Community Forum, and by leaving reviews on product purchases - at a rate of 0.05 of a credit per post and review.
Plus credits never expire - unless you cancel your membership. When a membership is cancelled credits are removed at the time of cancellation. However, any credits earned by participating on the forum or leaving reviews will not be removed.
You can see how many Plus credits you have in the top right corner of the screen under your name. The number next to the P symbol is your total number of credits.
Plus credits should not be confused with Store Credit, which is a method of payment used to purchase regular marketplace items. You can read more about that here.