Install Blender
Install Sims 4 Studio
Install a mesh editing add-on if needed
Choose the type of CC you want to make
Export a base game mesh or template from Sims 4 Studio
Open the mesh in Blender
Edit the mesh shape
Create or edit the texture in an image editor
UV unwrap the mesh if needed
Save the texture files
Import the edited mesh back into Sims 4 Studio
Assign the texture maps
Set the swatches and tags
Fix any clipping or mesh issues
Test the CC in Sims 4
Reopen and adjust if needed
Save the final package file
Place the package file in the Mods folder
Enable custom content and mods in game settings
Restart the game
Check the CC in Create a Sim or Build/Buy
Share the package file if you want to distribute it