Hey
I'm new in CC and I was made my first character. I see edges of body parts. How to smooth it or hide it?
In Substance Painter I see it too.

Did you use SkinGen? If so, can you show us the layers you used on the head and arms? Are you using decals? 

About SkinGen I don't know, I think I don't use it because I don't know how. I don't put any SkinGen Tools to body parts. 

There are some basic skinGen tools inside of CC3. You can purchase more advanced SkinGen tools in the Software Store.
The photo shows the skin panel. When you apply a Skin item to your avatar, it will take you to the skin editor.

Okay, thanks, but I still need help with this hard edges

It looks like it could be a skin saturation and or a Micro Normal Tiling issue. Under the modify panel try tweaking the Mico Normal and Blend Map settings to see if that fixes the issue. You could try checking the box for Flip Micro Normal Y under the micro normal section as well. 

And also see if you did not accidentally checked Flip Normal Y on Head (or other parts) for the Bump map.

hey, micro normal tiling it's good way! but I still see hard edges, I was try test different values with specular, roughness, flip Y and nothing

So those lines are due to the micro normal texture. When you have textures with a lot of patterns it can be pretty difficult to line them up at the seams. You'll notice a lot of those lines abruptly end at the seams because the other texture doesn't match up perfectly. Load any of the default characters and zoom in close and you'll see seams if you look close enough.

If you zoom out to a distance where the character will normally be viewed for your project, can you still see the seams? 

Gonna check it tomorrow