useradd

Basics

useradd -D -s /bin/bash        # make /bin/bash the default shell for future account creation (rather than /bin/sh)
useradd -m bob                 # create new user bob and create a home directory using /etc/skel as a template
useradd -m bob -k /path/to     # instead use /path/to as the template
useradd -m bob -k /home/alice  # bob gets a clone of alice's home directory

See also fun with useradd