You can compile any suitable document in the ITP/MDK Repository (i.e., Microsoft Word, OpenOffice.org and plain text) by right-clicking and choosing Create Model. Note that this option will be greyed-out if you have not yet configured the project. The first time you call Create Model, a model icon will be attached to the model document. It can be located as sub element of the model document if you click on the plus next to it so that it gets expanded. No matter whether compilation has actually succeeded, a model icon will always be created the first time you call Create Model. The underlying model will only be available for running after a successful compilation.
Anytime you create a model, you automatically get a lock for it. It does not matter whether you have created a model for the first time, or whether you call Create Model for a document that already has a model. After you get the model lock, no other user will be able to create this particular model. This is analogous to locking a document for editing.
The model you create is actually a private working copy. In the most likely scenario you probably have got some errors in your model document at first. You will then edit the source document and retry to create a valid model for it. This will overwrite the current working copy by a new version of the model. You can do this as often as you like. Other users (normally) do not see these working copies.
Only after a number of Create Model iterations and possibly test runs will you arrive at a situation that your private model becomes publishable. You should then unlock the model so that others can start using it. Unlocking will 'replace' the old public version of the model, if any. This is comparable to unlocking an edited document.