How do I write a validation rule?

[Tina Campbell]

how do I write a validation rule to require a 6 digit number in a field?

[ADezii]

I think that you are actually referring to an Input Mask. To force a User to enter exactly 6 Digits into a Field:

1. Create the Field in the Table and define it as:
   1. Data Type: TEXT
   2. Field Size: 6
2. Set the Input Mask Property to: 000000 (6 Zeros)