To use the realistic palm models: 

- Open your scene

- Go to File > Apend

- Go to the folder with your file "Coconut_Palm_Pack.blend" and select it

- Go to "Objects" 

Here you can select "Coconut_Palm01" and "Coconut_Palm02".

How to use the Coconut Palm Set for your background:

- Open your scene

- Go to File > Append

- Go to the folder with your file "Coconut_Palm_Pack.blend" and select it

To use the  group of palms go to "Group" and select "Palm_tree_group".

Go to your Render Properties, go to the Light Paths settings and set up the values for Transparency to 64 or higher.