Firstly, .schem are from 1.12.# and below while .schematic are from 1.13 and above. They are basically the same file, and the way you're going to implement them should be the same. Before you add the files to your server, make sure they are made for your server as they will either have blocks your server supports or not. 

 

1) Make sure you have worldedit/fawe downloaded on your server.

2) Add the .schem/.schematic file to your 'Schematic' folder that you will find in your worldedit/fawe folder.

3) go in-game and type "//schem load FILE_NAME"
(don't add the .schem or .schematic)

4) finally, you're going to do "//paste -a"
('-a' will not paste the air blocks. If you want them, simply remove the '-a')
 

If this doesn't work you can find many videos on YouTube that will explain it better :)
Just type "how to add schematic with worldedit"