Once an ITP Model has been successfully created for a model document, you can run it. You do this by selecting the model document or the model, right-clicking, and selecting Test. Note that this option will be grayed-out if you have not yet configured the project, or if the model has not yet been successfully created.
As long as you have a lock for the model, Test means running your private working copy of the model. This allows you to test various iterations of your model without bothering other users with it. As far as they are concerned, another user has locked the model, so they cannot create it, but they can still run the original public version of the model, provided it exists. This is analogous to editing and viewing a document respectively. Of course, you can also run unlocked models. This is straightforward.