Im kinda lost

[ElderChild]

I played Warframe a few years ago when it was fairly new. Now that I checked back on it I have the same problem. I am not sure where to start and what to do.
Let me try to explain. I kind of know which warframes and weapons I want to get later on an I know that there is a lot of different things to explore but where do I actually begin? Since there isnt much story going on so far I just feel like I am thrown into this game without a plan.
Are there...like certain steps into endgame? Coming from games like PoE and D3 I feel like its similar but in those games I know what to do next to reach my goal

[Gaardian]

Well, I'd work on getting your archwing if you havn't got that yet.

[Vulpesrojo]

Some things that might help you:
Complete any quests that you might have.
Complete planets by playing their mission nodes and killing bosses. The bosses will drop nav segments to allow you access to new planets. They also drop the parts to warframes, and, occasionally, weapon parts. Furthermore, as you unlock planets, new quests appear.
Complete alerts and tactical alerts as they appear.
Visit a relay. These are "safe zones," similar to towns. There are a few NPC units there that will give you some direction to go.
Join a syndicate or two. Their daily missions give you something to look forward to.
Buy some cool looking weapon blueprints and try them out; you might be surprised as to what you find.
Find some friends (or randoms) and play some void missions.
Find or start a clan.
Sell your soul to the RNGesus.
Profit.

[Green Spartan]

if you didnt had a ship before you left...try to asemble all the components of ya ship before anything else...then you can farm/do quests/praise to the eternal sun etc.