The recommended way to give students financial aid is to create a discount. This allows you to have more control over your data than simply issuing generic credit because you can associate discounts with specific Course Groups/Courses/Classes, with G|L accounts, can set start and end dates and can run the Discount Report to follow activity.
If you are using G|L accounts, make sure to set up the G|L accounts before setting up the discounts.
Next, navigate to Configure | Discounts and set up whichever type of discount you want to create (automatic or coupon). If this is truly financial aid, you might consider using coupons rather than automatic discounts and make them single-use coupons. This will give you more control over who is using the discount and how often the discount is being used. If you are associating the discounts with G|L accounts, be sure to select the appropriate G|L account when creating the discount. Remember that the G|L account you are associaitng with the Discount may not necessarily be the same G|L account that is associated with Courses/ Classes.