how to make software secure using VB.NET

Question

hello friends, i want to make my software secure i.e., I hace many forms in my softwares i.e., a textile erp but i dont want that every department see all the forms of the software. See, i want each dearptment to have priority. For example, Inventory department has no concern with the Forms relating to Accounts, so, there should be no form in Main Menu realting to Accounts if Inventory person logs in. So, buddy if you have any idea/suggestion/code then help me out as soon as possible. its my Final Project. My emails are: [email protected] [email protected]