In simple terms, locking cells is basically making sure that only those who are authorized to tamper with the data held by that particular part of the spreadsheet can actually do so. This can be done in a variety of different ways depending on the spreadsheet tool that is being used. Now, it is important to note that this is different from other methods of protecting spreadsheet documents against tampering. For example, it is a more specific option of making sure that a particular figure is not messed with than something like locking the entire document. In those kinds of cases, not only the cells, but the entire report itself will be inaccessible. Then there are cases with tools like Google Sheet where access can be shared. However, there are ways to make that access quite limited where you as the original owner will dispense editing privileges, as you please. In the case of locking cells, though, only that particular cell will be inaccessible. The rest of the sheet can be free game, but not the specific cells that are locked.