My geometry edithing doesn't work!

hi, I opend it in 3d thirdperson.
then I placed a cube, then I thied to used the tool geometry but if I select a block then it doesn’t become blue and I can’t select any side wath am I doing wrong? or is it a bug?

mc
,

Hello ,

If you’re trying to edit geometry within your level, please make sure that you’re laying down a ‘BSP’. These shapes allow you to edit the shape of the object pulled onto your level by clicking on the small boxes that are in the corner of the object.

The following links may help you with what you’re trying to achieve:

Cheers!