$ character introduces parameter expansion, command substitution, or arithmetic expansion. The parameter name or symbol to be expanded may be enclosed in braces, which are optional but serve to protect the variable to be expanded from characters immediately following it which could be interpreted as part of the name.
Read more in the Bash User Manual.
OpenStack is an open-source software platform for cloud computing. Linux instances can be launched/stopped manualy using the graphical web interface or automated thanks to ansible's openstack cloud module.
Configuring ansible can be tricky, but once well configured using it is really easy and powerfull for testing and Continuous Integration environment.