I wanted to change a feature attribute by selecting a feature in a vector layer and opening the feature form. The following QGIS online course does only show the procedure for an older version of QGIS: https://docs.qgis.org/2.2/en/docs/training_manual/create_vector_data/forms.html. Is there a way to accomplish the same in QGIS 2.18.9?
You can access this functionality directly from the Identify tool. Open the tool and check the box "auto open form". When you click the Identify tool again on a single feature, it will open form. Select multiple features and the usual window will open, allowing you to un-select the "auto form open" option. To set values in this form, you have to be editing the layer.