I need help how to solve this part of my project which is presented below. Could someone help me how to solve this?

The application has three types of users: Administrator, Manager and User.
The administrator logs in the system with their user name and password. he can
to add, modify, review and delete users.
The manager logs in the system with their user name and password. He can
review and regulate the offer for his travel agency. For each bid should
be able to add more detailed description. You can see and reported for each
The user is not logged into the system. He can review the bids and agencies
locations. You may choose to offer and apply by filling out the form
his personal data. You can register and retrieve email messages
offers from a particular agency.

If this is a web project use Session state to record the user's role. Then whenever access to a restricted page is required check the session variable to see if access is allowed.
When the admin or manager log in set the session based on their role:

Session["role"] = "admin";  // C#
Session("role") = "admin    // VB.net

or maybe you will enumerate and have numbers that specify the role, its up to you.
Then you can check it with things like:

If(!Session["role"].ToString() == "admin") {
  // redirect away from admin page