When requesting a ride, credits will usually be applied to your fare without you needing to do anything more. For business profiles, credits are toggled off by default, since most users don't want to use credits when riding for business. You can toggle credits on and off by tapping your payment method on the ride request screen and then the credits slider on the next screen.
Uber credits are non-transferable and do not expire. Uber credits redeemed with Uber Visa Card points can only be used in the U.S. Uber credits cannot be used when paying with a family profile or certain types of business profiles on Uber. Any available promotions will be applied to your ride before your Uber credits. Certain Uber credits may be applied to your ride balance prior to credits redeemed with the Uber Visa Card.