Draw and label the [100], [110] and [111] directions in a cubic unit cell

Given that

[100]:

It means that y and z component is zero. It is only in x direction.

[110]:

This is in x-y plane. Because z - component is zero.

[111]:

This is in a space because it have all three directions.

We take x is positive in right side, y is positive in upward direction and z is positive perpendicular to paper.

The following diagram we can easily understand the following directions.