First look at the pop is it a nail or screw. Wipe away all the excess dried mud or plaster to expose the pop. Then check and see if you can pull it out by hand, if so then do it. Your wall or ceiling will not fall down. If you can pull it out by hand you have a nail or screw that is not secure in the stud or truss and was not pulled out or popped in the wall securely.
If you cannot pull it out get h hammer and hit it back in the stud or truss, do not hit it hard. Next get yourself a 1 1/4 drywall nail and cap that nail. By capping I mean take a nail and place it on the side of the nail or screw that is exposed in the wall and pound it in where the caps of the nails or screws overlap. If it is a screw that is loose, get a screwdriver and screw it back in and cap.
Check to see it the wall or ceiling is loose. Hit it ever so slightly with the side of your fist. If you can hear it hit against the stud or truss then put a nail there to secure the sheetrock. If you hear a hollow thud then you are hitting the sheetrock in between studs and no nailing is required.
Once you have secured the nail or screw back in the ceiling or wall, brush away all excess sheetrock. Then get yourself some spackle and cover the hole flush with the existing wall and let dry.
When the spackle is dry, take a fine piece of sand paper and sand down the spackle smooth, flush with the ceiling or wall. Make sure you do not have any rough edges, these will show once you texture.
When sanded smooth you will need to see what kind of texture you will have to match. If the texture is in blotches the size of dime to quarter size then you have a knockdown texture. If the texture looks like an orange peel then you have an orange peel texture. When shopping for your materials find the spray texture can that fits your texture.
Read the back of the texture can and follow the instructions. The get your texture can and a piece of cardboard and spray sample sprays on the cardboard to match the existing texture. If it does not match when you spray it on wipe down with a wet cloth immediately. Let dry and paint.