One thing that I still get confused about writing is pivot queries. I find myself needing to lookup the syntax every time. Basically you use Pivot and Unpivot to change the output of a table. If you would like rows turned into columns you can use pivot and for the opposite you can use unpivot.
One thing to note is the column identifiers in the unpivot clause follow the catalog collation. For SQL Database, the collation is always SQL_Latin_General_CP1_CI_AS. For SQL Server partially contained databases, the collation is always Latin1_General_100_CI_AS_KS_WS_SC. If the column is combined with other columns, then a collate clause (COLLATE DATABASE_DEFAULT) is required to avoid conflicts.
Click through for an example of each.