It depends on the actions being edited and what plan you are on.
You can have multiple users editing different designs in a project. While it is possible to have two users edit on the same design, this can lead to some editing conflicts since you will not see the changes made by the other person until you refresh the design and may cause you to lose work.
On accounts with the Business plan, you will have access to the Design Locking feature that prevents other users from editing a design that a user is already working on. You automatically have editing control when you open an item in the Editor unless another user is currently editing the item. You release editing control when you close an item, you sign out of ProtoShare, or your session times out. Additionally, another user can explicitly take editing control.
If you have any questions, please let us know.