Here's how to create a measurement:
Start by activating the measuring tool by clicking on the symbol that looks like a ruler.
Left-click on the first point you want to measure from, then click on the points you want to include in the measurement by left-click.
End your measurement by right-clicking with the mouse. This will create your line. By clicking on the first point of the measurement again, an area will be created.
To add points to a measurement, click on a so-called "ghost point" between two points, which will create a new point for you. To move a point, click on it and drag it to a new position.
A tip here is that you can connect two endpoints to form an area by dragging one endpoint to the other. Additionally, you can right-click on a point and select Remove Point.
If you want to activate objectsnap measurement, allowing you to measure on CAD layers, areas, lines, and 3D models, click on the symbol that looks like a magnet under the measuring tool.