where do I add this files to the engine so I can use? .blend type? like save like download and save to use?
You can’t use that in the engine, it’s a file format that can be opened by the (free) program Blender
You would then have to export from Blender to either the .fbx format or .obj format (fbx preferred)
You cannot add .blend-files in UE4, you need to export them from Blender to FBX-format.
I export it as a .FBX, your next question might be why are the walls invisible from the inside, you can fix this by double clicking the objects material in UE4 and then tick the box that says two sided
A .blend file is a blender save file type that can not be used directly in the engine. You can open the file with Blender and then export the file as an FBX format, which can then be imported into UE4.
To import a FBX file, right click in the Content Browser withing UE4 and select “Import To…”, then find the FBX file in the dialog that opens.
umm I got this file from a web site I don’t know how to export to import ue4 so how to ? is it possible