The Jackal will most likely be the first boss new Tennos will have to take down. They are actually recommended to take down this giant machine several times in order to obtain the blueprints for Rhino, often considered the most beginner friendly Warframe thanks to his simple-yet-effective skillset.

By finishing quests in the codex, players can further progress the in-game story and, subsequently, unlock new game mechanics and even more power boosts. Be warned, however, as some quests for being tedious or difficult to complete, with one in particular taking over 3 hours to finish. 

While not necessary for in-game progression, joining a clan gives players access to a lot of powerful weapons and many other useful utility items. Creating a clan from scratch is NOT recommended, but don't worry, there are plenty of clans willing to take in new players

At its core, Warframe is a PvE game centered around finding out ways to obliterate your enemies in the most spectacular way possible. While there is still a "meta", the important thing is that you have fun when playing. Use whatever weapon or Warframe that speaks to you as a player!