1) For existing areas you can select the object and then drag on the small arrows that are between each two nodes. 
Or just create a new node by double clicking somewhere on the outline and then drag than new node to a new place.
(To go back to adding new nodes by clicking, you have to go through a relatively complicated workaround. But in case you want to give it a try *)

2) To create a hole in the parking lot area, select both the parking lot and the building inside (shift + click) and then press C to combine. 
(This will convert it into something called "relation" where the original outline will be an "outer" and the building and "inner" boundary.
You can verify that it worked by selecting the original outline, scroll all the way down in the left panel and then clink on the Parking Lot name under Relations.)


*) Workaround:
1. Select two nodes of the parking lot between which you want to inset points.
2. Press X to cut.
3. Select the small cut segment.
4. Scroll down in the side menu to find relations. And click on the trashcan icon to remove it from relation.
5.Press DEL key to delete the small segment.
6. Select one of the two nodes where you cut and press A. Now you can add nodes by single click.
7. Finish adding new nodes by clicking on the second node.
8. Select both split segments of the parking lot (shift + click) and press C to combine it to single area.
