There are a couple of ways,
#1 - use Format | Cells | Custom
and type in 00
that's zero-zero. Now all numbers entered will have 2 digits, and if you
type in a single digit, the leading zero will even be added for you. Use as
many zeros as you plan on having digits.
#2 - format the cells as text.
#3 - like #2, ends up with numbers as text in the cell:
prefix each entry with an apostrophe (')
Others should come along with other methods also. But those are 3 quick ways.
