We first see the F major scale in Lesson 10.  We learn that by following the major scale formula:

W W H W W W H

We get:

F G A Bb C D E F

The key of F major has one flat and that flat is Bb.  Its relative minor would be D minor.  Meaning D minor also has one flat and that is Bb.

This form was in Lesson 10 and a review of your 2nd position C major scale form in Lesson 4.

These forms are found in Lesson 23 and is the same shape as your 9th position C major scale form found in Lesson 20.