Speeding Up Repetitive Data Entry with AutoComplete
Excel's default setup enables an option called AutoComplete, which is designed to speed up entering data in lists. As you type, Excel compares each character that you enter with other entries in cells directly above the active cell. If the opening characters match those of any other entry, Excel assumes that you want to repeat that entry and fills in the rest of the label. (This comparison applies only to cells that contain text; AutoComplete ignores numbers, dates, and times.)
If you want to repeat the previous entry, press Enter (or Tab or any arrow key) to insert the AutoComplete entry in the cell. Keep typing to enter a new value in the cell. Excel will not suggest an AutoComplete entry unless the string that you have entered identifies a unique entry in the list above the active cell.
Tip from 
Instead of waiting for Excel's suggestion, you can select from a list of entries already in the column. To display the list, press Alt+down arrow, or right-click the cell and then choose Pick from List from the shortcut menu.
Some users find AutoComplete disconcerting, dangerous, or merely annoying because if you don't pay close attention, you risk accidentally entering the wrong data. You can easily disable AutoComplete: Choose Tools, Options, and click the Edit tab. Clear the check mark from the Enable AutoComplete for Cell Values box. Click OK to save the new setting and continue editing.
If you have a love-hate relationship with AutoComplete, create a macro that toggles this feature on and off. Assigning the macro to a toolbar button lets you turn on AutoComplete when you're entering data in a list where its capabilities are useful, and turn it off at all other times. Here's all the code you need:
Sub ToggleAutoComplete()
Application.EnableAutoComplete = Not Application.EnableAutoComplete
End Sub
→ For instructions on how to assign the macro to a toolbar button, see "Adding Macros to a Toolbar".
→ Don't confuse AutoComplete with AutoCorrect; for more details about this and other Office-wide Auto-features, see "Using AutoCorrect to Automate Documents".