Before you start a project, assign each user an area of the model. To prevent potential save conflicts, you need to avoid having more than one user working on the same, or adjacent model objects. See also Saving in multi-user mode.
If three users are to model a project, User #1 could model columns, User #2 the 1st floor beams, and User #3 the 2nd floor beams.
In the following example, three users are working on the same model. You can see how modeling and saving works in practice.
The master model contains columns and grids, as you can see here.
Each user opens the model in multi-user mode. All users are now working on working models, locally.
On the working models:
User #1 adds base plates to the columns:
User #2 adds and connects the 1st floor steel beams:
User #3 adds and connects the 2nd floor steel beams:
User #1 clicks Save to save to the master model. His working model now shows the base plates he added and looks like this:
User #2 clicks Save to save to the master model. His working model now shows his 1st floor framing and User #1’s base plates:
User #3 clicks Save to save to the master model. His working model now shows all three users’s work:
To see the updated master model, Users #1 and #2 need to save to the master model again to update their working models.