Not everyone wants to join a gym to achieve their goal. And you don't have to.
You can work out at home or outdoors, at the gym or at a club.
However, wherever you plan to work out should be reflected in your workout plan, as it has a strong influence on the choice of your exercises.
Lots of exercises can be done outside or with little effort at home.
Functional bodyweight exercises, in which you do your workout with nothing but your own bodyweight, are just one of your options.
You can think about purchasing fitness equipment like kettlebells or dumbbells if you plan to work out on your own long-term.