I made a uv map in blender, but when I export the fbx to ue4, the area or material I mapped just shows up white. what can I do to fix this?
Have you imported the textures and created the material in UE as well ?
When you create UV map, you just assign each vertex in your mesh some UV coordinate. So when you load and image and use it as a texture, each vertex knows where on image he is supposed to be. So if you exported only you mesh as .fbx, you have to create material with some texture and apply it to your mesh for you to see.