Dynamics NAV comes with object level permissions. You can setup what objects (tables, reports, pages, etc.) each user has access to and specify if the data can be inserted, modified or deleted.

If you want to control permissions down to a field level (e.g. who is allowed to alter what field) then you need to get an add-on for this (which there are many to choose from) or develop something yourself (which is quite easy). The same goes with if you want to control what user that is allowed to post onto what g/l account, location code, item, bin, etc…