Missions

There are a lot of planets, all with a bunch of their own missions and each mission can have its own variants.

The mains types of missions are:

Exterminate (basically kill everything)

Defence (stay in one area, defending a target from enemies lasting 5 rounds at a time.)

Survival (stay in the mission as long as possible, rewards every 5 minutes)

Rescue (break into a area and rescue and extract a hostage)

Spy (try to sneakily get through and hack 3 vaults without losing the intel)

Mobile defence (hack and defend 3 consoles from enemies)

Interception (control 4 territories from enemies)

Assassination (killing a boss)

Sabotage (sabotage enemies supplies)

Capture (find and extract the enemy target)

There are also 3 open world free roam missions, one on Earth called Plains of eidolon, on Venus called Fortuna, on Mars called Deimos.

Each of those missions are used for Void fissure too missions in order to get primes.

If you want a full guide to quests check out https://www.warframe.com/game/questguide for an in dept step by step guide for every quest and what order to do them.