[Brand new player here. Any advice?]

When first starting the game, many things will be pretty confusing, but if you make sure that you follow the main mission, as well as making sure that you farm for basic items such as Warframes (like Rhino or Valkyr for example), you will be able to rank up as you play. I would recommend you do not get attached to just one weapon or one Warframe, because you would obviously not be able to further your rank into the game and have access to better weapons/Warframes. Now, if you need help, I would also suggest getting that from your friends, or from someone who has played Warframe for a long time. When you go to ask a question in the community chat, it will most likely not get a straightforward answer.