Is it necessary to join a gym for building 6-pack abs?
The most necessary thing for six-pack abs is eating well. The saying has always been is abs are made in the kitchen.
Let's step back.
Everyone has abs. Regardless of whether or not they work out, the rectus abdominus muscle that forms the famous eight-pack of muscle criss-crossing the front of the human body is there in every single one of us.
The primary question is what is covering yours? If it is a thin layer of skin with minimal subcutaneous fat? Then congratulations, you probably already have a six-pack.
If there is a decent amount of fat there, then it's unlikely you'll be seeing your abs any-time soon.
It takes a well-managed diet maintained consistently over a substantial period of time to reduce body fat to sufficiently low levels to see abs all the time. That is a challenge.
You can also build the abdominal muscles. This is done using weight or core exercise. But if you're 300lbs and 30% body fat, however strong your abs are you won't see them.
Start with the lead domino.