Tab is a fixed indentation or space.
On a standard keyboard, it is above CapsLock on the left hand side of the keyboard and has two arrows (one pointing either way).
If you put in your number, then press "tab" and then beging typing again, the space between the number and the text will be a fixed amt.
So, you can have a list of numbers:
1 number one
2 number two
3 number three
10 number ten
and so on.
When you get into double, triple figures, the beginning of each sentence will be in the same place.
(I hope this has not confused the issue...!)