Somewhere on your sheet, create a range containing all the Sheet names in your workbook. For instance, "Sheet1" in cell A1, "Sheet2" in cell A2, etc.

Then from the main menu, select View, Toolbars, Control Toolbox. Use the Control Toolbox to put a Combo Box on your sheet. Right click on the ComboBox, select Properties, and set ListFillRange to the range containing your Sheet names.

Then double-click on the ComboBox to get to the Visual Basic Editor. In the Worksheet object, enter the following vba code:

Private Sub ComboBox1_Change()
ThisWorkbook.Sheets(Me.ComboBox1.Value).Select
End Sub

If you're not familiar with vba (Visual Basic for Applications), or with using the Control Toolbox, you must learn to do so in order to accomplish this task.