When labelling areas in QGIS I can't figure out how to display the unit after the number value from a field.
For example the area of my polygon might be 1.23 hectares, which has been calculated using field calculator $area/10000.
How do I then display, for example, 'Ha' after the value, or do I find the tool to do so in the labelling options on the layer properties?
In QGIS go into the layer properties > label tab.
Click on the expression icon 
on the right hand side of the 'Label with' field.
In the left hand expression window enter
"your_area_column_name" || 'ha'
You can go further; if you want to have a label, for example a woodland name, with the area of the woodland on a line underneath then use
"woodland_name_column" || '\n' ||"your_area_column_name" || 'ha'
The '\n' introduces a new line into the label
Note: Rather than type the attribute column name into the left hand expression window you can use the middle list of 'values' to select it. Expand the Fields and Values and double click on the field that you want.
Assuming you are using ArcGIS:
You can append units to your label using a label expression. Open the Properties of the feature class/shapefile you are trying to open, from the Table of Contents. Click on the "Labels" tab. Click the Expression button to open the label expression window. From there create your label expression using your desired parser.
For example if you are using VB and your field name was AREA, your label expression would be:
[AREA] & " Ha"
