Add material to a mesh
1. Select the mesh
2. Object Mode
3. In the properties window, select the materials tab (2nd from bottom, circle icon)
4. Delete irrelevant materials
5. Add new (+ icon)
6. Under Surface dropdown, click base color button
7. Select "Image Texture"
8. Select path to your texture image.
9. Visit different layout if you arent seeing it
Export to Unity
1. Limit to selected objects
2. Forward - Y Forward (or whichever way the object is facing in blender)
3. Uncheck "Use space transform"
4. Uncheck "Add leaf bones" in armature section
5. Import into Unity "Import New Asset"
If its facing the wrong direction:
6. Click Model tab in Inspector of the fbx outermost file
7. Check "Bake Axis Conversion"