User sections are non-standard profile cross sections. They are drawn using AutoCAD elements. After creating a user section it may be used the same way as any other section in the system.
Once created the User profiles are saved in: C > ProgramData >Autodesk > Advance in the AstorProfiles2017.mdb.
You can delete a USR_ profile or USR_Userdefinedtreads from the Access Database > AstorProfiles2017.mdb.
You can also remove them from the 2017 Advance Steel Management Tools.