There are two ways to add tiles into a collection.
1.If you have already started a collection and you want to add in more links whilst in the folder, you can do this by pasting in a URL, followed by an image/colour and a title. See the article here.
The other way to do this, is by moving and transferring a Tile from either My Tiles and Workplace.
Here is how to do it:
Step 1. Go to My Tiles
Step 2. Select the drop down ellipses
Step 3. Choose the folder where you wish the tile to be exported.
Step 4. Click Save
Step 5. The tile has now saved in your chosen collection.
Follow then same steps if you wish to move a tile from Workplace.