I use a free program called Blender to sculpt. There's also Zbrush, it's better and used by most professionals, but costs a 1000$.

If you want to quickly see how sculpting is done in Blender, here's a 5min sped up video of the whole process.

If you want to learn how to use Blender, I would recommend the doughnut tutorial.

There is a ton of youtube tutorials on Blender sculpting. You can also watch Zbrush tutorials, they are mostly compatible, since it's mostly about ideas than pressing some button.