When you have questions about a challenge you can use the ask for help option.
But since you already started this topic it would really help us out if you could provide us with the link to problem you are referring to. It sounds like you are somewhere in the applied visual design section.
Offset means to move away from something. So if the instructions say “offset it 0 pixels from the top” that means you start at the top and move 0 pixels away from the top (i.e. toward the bottom). So in your CSS you would use the top property and then the number of pixels you set for top would be the number you move away from the top (0 in this case). So the correct answer would be
top: 0;
In CSS, the value you give top is the offset. This works the same for the CSS properties bottom, right, and left;