Place a Custom Model
Placing via command
To place a Custom Model, you can use the command /custommodel spawn <name|uuid>. Make sure that the Custom Model has a way to be removed, otherwise you will have to remember the entity ID and delete it with the command /custommodel kill <id>.
Placing via script
You can do this with the Spawn Model node.
Placing with Custom Block
Custom Blocks have a property dedicated to this. See the guide dedicated to this.