WEll first of all, your hub may not require packing. Only hubs running loose bearings require packing. If indeed your hub runs with loose bearings...
Fill the groove with grease, insert the the loose bearings. You want the grease to make a "trench" for the bearings. When you place the bearings, there should be enough grease that the bearings stay up. You should not have to repack very often, unless you do a lot of rides in rain and/or mud.
Your hubs may run sealed cartridge bearings, which is the most common way bearings are found. In this case, you don't need to do anything and they will last a very long time. If by chance these bearings are shot, you simply replace the whole assembly