By default, when you create a numbered list, it starts with 1. Also, when you create a lettered list, by default it starts with "a". Sometimes, though, you might need to start your list with a different number or letter.
Creating A Numbered List In Word
Initially, you have to create a standard numbered list in Word. You can do this in a number of different ways. The quickest and simplest way is to type "1." and then press the tab key on your keyboard. Word interprets this as a command to start a numbered list, and indents your text appropriately. Alternatively, you can go to the Home tab and click Numbering in the Paragraph group. This will display "1." and indent it in preparation for you typing out the first item in your list. A third way of creating a numbered list is to type out your list items first, pressing Enter between each one, then select them all and click Numbering in the Paragraph group.
Whichever method you choose, create your numbered list. Then select the entire list and right click > Set Numbering Value.
In the little window that opens, ensure that Start new list is selected and then amend Set value to the starting number.
Lettered Lists
The above process is also true of lettered lists. Similarly, you can start a lettered list by typing "a." and then pressing the tab key on your keyboard. Word interprets this as a command to start a lettered list, and indents your text appropriately. As above, once your list is typed out, select it, right click > Set Numbering Value. This time, you get a choice of letters to start your list from.