Rotate marker symbols individually in QGIS

Use Data defined override. Go to Layer Properties and in Simple marker style open the Data defined override menu with icon next to the Angle value. Choose Field Type -> "your column".

Data defined override button:

Select column:

Result:

If you select Edit... in Data defined override you can also insert a custom expression.

If u want rotate symbol for a specific Category go style -> change symbol method to Rule-Based ->add new rule like "column" = 'something' and chose rotation angle

Edit: solution to your problem: click icon next to rotation input field -> click edit (under "Variable") -> type "column"

Where "column" is the name of column where angles are defined