There are not only just one type of quest however there are different types and in this guide I'll describe the different types which will help you understand which ones are right for you.
The first type you'll notice is the storyline type.
This is the main story of either The Guardians or The Defiant.
Most of these are solo type missions for you to go through alone however you may end up in a position here you may need the help of some more people.
You are given rewards for completing these missions and you can also get yourself some rare rewards for completing off storyline missions in the game.
As you play though you may notice that you receive more missions available as you complete other certain missions.
As mentioned you will receive many rewards for the completion of the quests including experience, items, soul rewards and more which you may find useful later on in the game.
The next type of quest which you may be interested in is the dungeon type.
Unlike the storyline type this type of mission is one that needs group help.
As for your group you will need one that is well rounded; a healer, a defensive player, someone who can attack from long range and someone who can deal a lot of physical damage.
These are the main players you'll need in your group and you may also need more of one type of person too.
The goal for this type of mission is defeat the bosses and obstacles that come at you.
It is a fun type of quest to play though especially if you have a group of friends on the game already.
Make sure that before you start with your journey that you get all the quests from the questing hub.
This will help you save some time on the game and will mean that you will also level up through the game even faster.
I recommend that you only do one of the rift quests at a time as this will save you time travelling around and trying to complete multiple ones at a time.
You should try to make sure that you also complete them in one area first so you don't waste your time travelling to different areas of the map just for one mission.