Hi juma48 and welcome to Geeks to Go!
The below information should help you with your problem:
1) Password to open
Requiring a password to open an Excel document is the most radical method of document protection. The author of the document forbids access to anyone who does not know the password. This means that a user who does not know the password will not even be able to see the contents of the document, since the password is asked for when the document is being opened.
You can set a password to open either for a new document (Save As > Tools > Security Options) or for an existing one (Main Menu > Tools > Options > Security).
2) Password to modify
Suppose a document contains information that can be viewed by anyone, but should be modified only by a limited number of users. In this case, the author requires a password to modify. A user who does not know the password can view the document and make changes, but cannot save these changes to the document. However, you can get around this type of protection by using the "Save As" command and saving the document under another name. The password to modify will be reset in the newly-saved document.
Use the same procedure to set a password to modify as is used to set a password to open.
3) Sheet protection
As you may know, an Excel document can contain several sheets, and each can be protected against being modified with a unique password. In addition, while setting this password, you can specify the items in this sheet that can be modified by those who do not know the password. This method is widely used for form sheets. One area of such a sheet normally contains static information or hides calculation formulas, and the source data for that area is obtained from the form filled in by users. When a sheet is protected, a user can view the information in the document and make calculations according to the algorithms provided by the author of the document, however the user cannot modify the sheet or copy the information from the sheet without knowing the password.
You can set a unique password to protect a sheet from this menu: Main Menu > Tools > Protection > Protect sheet. Items that can be modified without knowing the password (Contents, Objects, and Scenarios) are also specified in this window. You should select these items as needed and confirm your choice by clicking OK. The password is reset using the same menu item.
4) Workbook protection
If an author wants to protect the structure of an Excel document, the Protect Workbook option is used. This type of protection prohibits the user from adding, deleting, moving, hiding/unhiding, and renaming the sheets of a document. This password is applied to the entire document.
A password to protect the workbook can be set from this menu: Main Menu > Tools > Protection > Protect workbook. This window allows you to protect the structure and the window arrangement of the workbook. You should select each option as needed and confirm your choice by clicking OK. The password is reset using the same menu item.