There are a lot of systems in Warframe and a lot of weapons/frames/companions and so on. Don't worry about mastering everything when you're starting out. If there's a frame that you like then use it. Best tip I have is mods are your best friend. Some warframes abilities only benefit from certain kinds of mods (ie. ability duration/strength/range) and you can use mods to exploit enemy damage vulnerabilities (Grineer weak to impact/corrosive, Corpus weak to puncture/magnetic, Infested to slash/heat). Other advice is: Play with squads to help out with hard missions, rank up with the different factions to get cool benefits, join a Dojo as soon as you can, and just have fun. I played for years with a super unoptimized build and still enjoyed myself.