Hi Acowaz,
In Excel, all cells are formatted with protection set to ON by default. All that's needed to activate the protection is to protect the worksheet, via Tools|Protection|Protect Sheet, leaving all of the protection options checked. You can use a password if you want.
Once you activate the protection with the 'Contents' option checked, users won't be able to edit any of the cells. From your request probably don't want to do that. So, before protecting the worksheet, use Format|Cells|Protection and uncheck the 'Locked' option for all cells that you want the users to be able to update. Depending on your worksheet's layout, you might find it quickest to unlock all cells on the worksheet, then lock only the ones that need to be protected.
Cheers
Cheers