Hi Miguel Figueiredo,

First of all i will tell you about group creation.

1)We can define collection of groups as hierarchy (known as application), will be shown as selection in user settings.

2)Define a single group with out hierarchy, which will be a checkbox in user master.

Here you can use second option.

First  you have to define view, action, menu for your transient model then mention parent menu for it.

Then include the above created group in the menu you created and parent menu.

Finally enable group in user master for the users you want the menu to be visible.