Hi and welcome to AirlineSim!
If you haven’t found it already, read this guide that’s often recommended to new players to learn the game mechanics: AS for beginners - an attempted blog
That’s not really true - the very old game worlds usually have few players, but they’ve got very large airlines by now and so there’s not necessarily that much space left.
Younger game worlds (especially Yeager, Otto and Quimby) may have many players, but the airlines are still small, so it’s generally easier for new airlines.
Still, even (or especially) old game worlds can offer great opportunities, because it’s all about finding the a niche or jumping in at the right time, as there will always be some players who quit the game and leave a lot of room for start-ups again.
If you got more questions, you may also want to join our Discord sever and maybe get some quicker feedback for your airline, when you need it.