Post moved - please read the section descriptions to determine where best to post.
You don't say what version of Archicad you are using - labelling methods have changed in newer versions.
Ideally add your operating system and Archicad version to your signature so you don't have to type it every time.
Answers to your questions can be version and operating system dependent.
In 20 you label on the elevation just the same as you do on the plan.
Select your label and click the element (window).
One of the forum moderators.
Versions 6.5 to 25
Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10
Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10