*a number*means we choose an arbitrary variable, let's call it x.

Twice a number means we multiply it by 2.

2x

Six less than that means we subtract 6

2x - 6

Now, the last piece, we set up an inequality. At least -1 means greater than or equal to 1. At most 1 means less than or equal to 1. Notice, for both points, we include the number.

-1 <= 2x - 6 <= 1