O = r - 1
I’m not sure how to do one step equations

Assuming you meant 0, and are trying to find r.
To find r you have to get rid of the -1,
to do that you have to add 1 to both sides of the equation. This will get rid of the -1 leaving r by itself because -1 + 1 =0, and the 0 will become 1 because 0+1 = 1.
Now you are left with
1=r