how to gain levels beyond 400?

[queen fossil]

New to game and reached 400, dunno what to do now (havent done weeklies and not sure what kind of weeklies are there)

[onyx kettle]

Kell's fall with as many modifiers as you need to bring up the reward to A rank

[midnight elk]

Any portal ops GM resulting in A grade has 5% chance to drop a prime engram with some bad luck protection built in. Zavala gives 2 gear pieces at higher power weekly