Windows PowerShell™ is a task-based command-line shell and scripting language designed especially for automation of Windows tasks. It has become the defacto CLI for Microsoft products since the its release, and can fully leverage .NET frameworks.
With the release of SQL Server 2008, SQL Server PowerShell was introduced. It is a powerful tool that can be used to automate many repeative task. You will also see some folks that use it for deployment and to standardize tasks/objects across many servers.
Powershell is also able to use .NET frameworks, which is especially handy for SQL Server when using the SQL Management Objects API. Some starter links on SMO are here:
SQL Server PowerShell offers some information regarding use of PowerShell within the context of SQL Server.
As always you can read through the FAQ to get general ideas of how to ask your question. Any question you do post regarding PowerShell on this site should involve SQL Server in some manner. This can include working with SQLPS or SQL Server Management Objects (SMO).