Create a second camera GameObject>Camera.
Rotate the camera 90 degrees in the x axis. and set the projection to Orthographic.
Set the size so that the camera shows a decent amount of the game world. You can check this in the camera preview.
Set the camera depth to 1 so that it sits above the game view camera. (The depth numbers act like layers the higher the number the further up the pile)
Position the new camera by changing the Viewport Rect settings.
Something similar to the settings above will give you this effect.
Now we need to get the camera to follow the player. Parent the new camera to the player game object.
Now we need to set the player and camera position to the same. This is very easy to do. Select the camera and in the Transform component in the inspector click the settings icon (cog). Select reset position. This will place the object at the same position as its parent.
Now move the camera up in the Y axis so that it is above the game world. Test your game and the camera should now follow the players movements. You may need to rotate the camera in the z axis as well to get the desired effect. Finally remove the Audio Listener from the camera.
Adding the player icon. Create a PNG icon with a transparent background. (This example is 128px x 128px). Import it into Unity.
Select the imported image in the project window and in the inspector check Alpha is Transparency.
Now create a new material Create > Material. With the settings below. Attach the icon you just imported into the Albedo section. make sure you check Emission and selct a colour to emit. This will make the icon show up on the miniMap.
Create a Plane game object. GameObject > 3D Object > Plane. Attach the new material created and scale it down so that it works well with your camera view.
Parent the palne object to the player so that it follows the player just like the camera. Reset the position and sort the rotation. Finally move the plane above the player and turn off cast shadows in the inspector.
Test your minimap and you should have an icon that follows your player.
Adding a border to the minimap. Create a new canvas and set the Render mode to Screen Space - Camera, and set the Plane Distance to 1. Attach the minimap camera to the Render Camera slot in the inspector.
now add a Panel to the canvas. GameObject > Panel. Uncheck Fill Center and set the colour to whatever you wish.
You should end up with a very basic miniMap.