There are two ways to go about this. When you launch the game, you get the option window before the game can start. At the top there is a dropdown for tools. One of them is ship catalog manager. Use this to import the sment file to starmade.
The other way is to take a program like winrar or 7zip, open the sment file and extract the contents to the blueprints folder in your starmade directory.
After that it is a matter of using the admin catalog in game to spawn in the station. Seeing as it is a sment file, I believe it will actually spawn in as a ship. I cannot recall if stations have different file names. If you cannot find it in the catalog use this command.
/load "name of blueprint" "name that you want for structure"