Depending on your liquids thickness you can drip 3-4 drops into your 510 atomizer. Depending on how long of draws/hits you take 4-8 hits you will need to redrip. Long hits-4-5, short hits you can go longer between dripping. The taste and vapor production will let you know when you need to re-drip. At the slightest hint of a harsh hit-re-drip. Keeping the atomizer moist with juice is the key. Make sure to have back up atomizers as you learn to drip.
You can use the cartridge without any filler and it become just a mouthpiece. Most of us use Drip Tips which can be purchased almost anywhere you buy your supplies. You really should search around for good prices and think about which material you may like best. Some drip through the drip tip-some take it off, drip and replace. Most drip tips out there will hold some juice in the tip when dripping through them-just be sure to give 2 quick blows (mouth not touching tip) to force the juice on down.
Pic of some of the tips out there: