what do you mean x?
the button you press is 8 and then you click your builder guy and choose a building to build
but when i do that the game shuts down
the button to turn the instant build on is 8. then when u pick ur builder and then a building. put it where u want it. then select the building and hit x. do not hit 8 again unless u want to turn the opition off. pressing x is what builds the building make sure your working is already working on the building before pressing x or u might not get a working building.
i turn the build opition on when i am on the camp map. then just use x to make the builds pop right up once the worker starts working on them. u only need to press 8 once then use x to build the buildings once their hit points start to increase.