How do I make a model placing System?

Step 1: Create whatever models you want placed.

Step 2: Make a script that does two things: a. clones the Master Copy of the model that you want to place b. moves the model to wherever the mouse moves; moving models can be done using primary parts.

Step 3: Fix any bugs :)

Make sure that you correlate local scripts and server scripts respectively for whatever task you need. Remember that local scripts should only be for the player to see something, but changes to the actual server itself and that could affect other players should be handled by server scripts.

Hope this helps! Feel free to learn more about models here!