"What is
juice?" is a very basic question. I recommend that you read my Wonderful World of
vaping illustrated guide in the ECF Library, especially Parts 1 and 3.
Drip tips and the eGO came out after that guide was written. A drip tip can be used with almost any atomizer
instead of the cartridge. As the name implies, its purpose is to enable convenient dripping (which is an alternative way of feeding e-liquid to the atomizer). This is not something you need to be concerned with when you first start vaping.
The eGO (and similar models) is a new high-capacity battery for the extremely popular Joye 510 atomizer. It
can be used with a drip tip but it doesn't need one.
If terms like 'atomizer', 'cartridge', and 'battery' (and how they work together) are unfamiliar, also read Part 2 of that illustrated guide.