Mastery rank.

[(XBOX)Random Brit7900]

I’ve just completed my mastery rank 5 Test. I have no clue how mastery rank works, And I haven’t gone to mastery rank 5. Are there any other steps I need to complete? 

[Graspier]

You probably pressed practice and not "begin test" 
I did that once too, and when I came out of the test, I was confused but figured pretty much that I did practice and not the actual test.

Do it again but this time make sure you click begin test

also, in case it is like, you gave the test but still didn't advance to the next rank and it doesn't show an option to retake the test, contact the official support team of Warframe, as players are unable to help with this matter.

Have a great day ahead and hope this helps.

[AltairFerenc]

leveling up weapons, frames, companions(only once) gives you mastery xp, your mastery rank dictates how many times you can trade a day, how many standing you can get a day(for each syndicate) and some weapons are MR locked and you can't use them until you reach that rank.

[Protector2707]

maybe you press into practice and not on the actual test

[Toemoesh]

You get Mastery xp for lots of things: leveling up your items to level 30, completing nodes in the star chart, doing missions. The mastery challenge itself can be done as practice or as the "real thing". When you're eligible to rank up you'll see it when you open your menus.

[(PSN)Claudija]

3 hours ago, AltairFerenc said:

leveling up weapons, frames, companions(only once) gives you mastery xp, your mastery rank dictates how many times you can trade a day, how many standing you can get a day(for each syndicate) and some weapons are MR locked and you can't use them until you reach that rank.

It affects base mod capacity, Syndicate Daily Rep Caps, Void Trace capacity and Focus daily cap as well- just checked a screen I made to show a friend I passed MR21 and those four items are listed.