What kinds of things does security deposit cover?
Can it be used for rent, carpet stains, cleaning, mold, stuff like that? And what about if the tenant stayed an extra two days, can I deduct that from their deposit?
The security deposit can be used as collateral against any damage (outside of normal wear and tear) and/or missing items/fixtures as a result of tenant accidental misuse, neglect or intentional behavior (their guests/relatives included).
You may find a few states that permit the use of a security deposit toward the rent, but many do not and will require it to be returned within a certain amount of time. And if any of the money is to be withheld, some states will also require an itemized statement to be given to the tenant.
Learn the laws regarding collecting and returning a security deposit here: