GIMP Add border and shadow to a layer

To Add border to layer follow below steps

1. Select the layer then use menu "Layer -> Transparency -> Alpha to Selection.
2. "Select -> Border" Border Selection window will appear. Enter the size of border you want to show.
3. "Layer -> Transparency -> Intersect with selection"
4. "Edit -> Fill with FG/BG Color" You need to select required color from FG / BG color panel.
5. "Select -> None"

With above steps you will be added border to your layer.

To add shadow to layer

1. Select the layer 
2. "Select -> All"
3. "Filters -> Light And Shadows -> Drop Shadows"
4. Window will appear select / add required values and click on "OK"