The most commonly known cmdlet out of this module is, Invoke-Sqlcmd. This is generally thought of as a PS replacement for the old sqlcmd command-line utility, that to date is still available in currently supported versions of SQL Server. You utilize this cmdlet to execute any T-SQL query that you want against one or multiple instances. The advantage you get using Invoke-Sqlcmd over the command-line utility is the power of handling output in PS. The output from the cmdlet is created as a DataTable (System.Data.DataRow is the exact type).
This is a good overview of the different methods available.