Agnes,
It is important, if not essential, that you modify your profile (Profile link above) to give the version of ArchiCAD that you are using, along with the computer specs etc - as you see with most other users here.
The method that Dwight gave is the easiest method for versions 10 and greater. Works with the Beam Tool as well as the Wall Tool.
Duane's method (slabification) is what you should use for versions 9 and earlier.
There are a couple of other notes I would add about each method. With the Complex Profiled wall/beam method, you may have your 'wall' of letters interfere with the wall that it is intersecting. Either pull it slightly away from the wall if that happens, or change the intersection priority.
Duane's method gives more control over the materials of each letter, if they should differ (which they do not in your screenshot). If each letter should have a different face color or material, you can only accomplish that with the complex profile method if you extrude each letter separately. All edge/side surfaces of a complex profile can be unique - but the ends (faces here) are unfortunately a uniform material.
Cheers,
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB