How to run addtional Shells on top of the default shell

view story

http://www.unix.com – Hi What is the command to run additional available shells on top of default shell. I am using bash also how can i tell that the additional shells are actually running? Also what is the advantage of running additional shells on top of your default login shell of bash? Lastly How can I terminate the shells I opened What would happens if i accidentally closed the default login shell? Thanks Bill thompson (HowTos)