Gravity wants to accelerate you at $9.8 m/s^2$ downward when you are standing on a scale. The scale, which is on the floor, which is on the Earth, wants to resist your downward acceleration. So, the scale must resist that acceleration with a $Force = m*9.8 m/s^2$. It shows up as your weight on the readout.

**Even though you aren't moving, you are still being subjected to a gravitational acceleration**.