What tool do I use to make a part smooth I have what is on image 1 (the black colors), and i want it to be like the image 2 (orange color legs)

I know that there a tool that can do it but i can't find it.
It's the subsurf mod! https://docs.blender.org/manual/en/latest/modeling/modifiers/generate/subdivision_surface.html
Extra characters to fill answer quota.