The simplest way to achieve that is to:
- prepare the list next to your table or on other spreadsheet (just input all available values in a column) – it’ll be a source for your list of values and it may be hidden later, if you want
- mark a cell (or a range of cells) in which list should be displayed
- select Data > Data Validation > Data Validation
- select Allow: List
- indicate the list prepared before as a Source. In Source you can enter any values you want separated by a comma.
- confirm
The drop-down list is ready. For combo-box you should use VBA, I believe. But you may also use the method described above and e.g. prepare just two-elements list containing “Yes/No” or “True/False“, which is generally the same.
The method should work regardless of Excel’s version.