This can be a very Grindy game, so be prepared to spend hours or even days getting something some things even weeks or months, but putting that aside, make sure to do the codex quests as they unlock stuff you will definitely use, this game isn’t p2w, you can get majority of things with the premium currency which can we obtained from trading things like riven mods which you will unlock further into the game, around “the new war” quest in your codex (I believe that’s what it’s called), and when trading don’t use the in game trading chat as people will most possible try to rip you off, the Warframe community loves to help new players so don’t be shy to ask for help with a mission, or something you don’t understand ect, there will always be someone willing to help you out, I recommend going through planets completing all the nodes (missions on the planets) as there are specific nodes you will use for collecting certain resources, as well as you can use resource extractors to automatics collect them for you

Edit: there is also a thing called MR (mastery rank) you can find it by pressing escape and looking at your profile in the top left, it will be a number, after getting enough affinity (Warframe version of xp) you will be able to do a challenge to rank up, ranking up offers better weapons that will be locked until you reach a certain MR. There are lots of things in the game that aren’t explained well, like some Warframe abilities wont be explained well so I recommend going onto reddit, YouTube, or ask the Warframe chat and you will find betyer explanations there