I've leveled up once and it took forever. Is there a faster way to do it? I've just been doing missions over and over again and am only level 1 with a tiny bit of xp. I'm noticing that the Venus missions recommend level 5+ but at this rate I'm not even close.
That number is your frame level, or rank. I just dinged 2 on my actual level and had to beat a trial mission or lose my progress. The only benefit I see from hitting 2 is being able to purchase more blueprints.
To level up mastery (account level) you just have to level up warframes and weapons. Weapon level ups give 100 mastery xp, while warframe level ups give 200 mastery xp.
The starter braton and starter Lato don't give any mastery xp until they reach a certain level, since they are extremely cheap. This is to prevent people from getting the first 5-10 easy levels quickly, then sell it for another for another 5-10 easy weapon levels each.