When you use a password to protect a Sheet in a spreadsheet the cells that are set to be protected or protected and hidden are operated on as a group. You cannot select just say one cell to be made visible by using the password; the whole group will become unprotected.
You can however do this with a macro. I have attached a sample spreadsheet using a macro that only shows one cell. Cells B1, B2, and B3 are protected and hidden. Select one of the hidden cells and click the button and that cell will become visible but still protected so that it can be seen. When you close the spreadsheet do NOT save as this would save it with the cell you have made visible remain visible. If you want to change the data in one of the protected cells open the spreadsheet and unprotect in the normal way, make the changes and protect. The password for my example is retep, you will see it used in the macro.
You should be aware that protecting sheets with a password is not really secure. It is meant to prevent inadvertent modifications. The spreadsheet is not encrypted and can easily be seen without the password. Do not let anyone have a copy of your spreadsheet as they could see the sensitive information without the password.