[fintstone]

The 1-15 are grades (relative rank). The grade is determined by the position, not the quality or actions of the person filling it. It is based on the skill, experience, and education required to perform the job. If you fill a GS-3 secretary position by hiring a PhD nuclear physicist, they will still be a GS-3. If they stay in the same job for 100 years...they will still be a GS-03.
The steps are determined by longevity in that grade and adequate performance. The person must wait 52 weeks to recieve steps 2, 3, and 4; 104 weeks for steps 5, 6, and 7; and 156 weeks for steps 8, 9, and 10.

You start with 4 hrs of vacation per pay period (2 weeks). There are 26 pay periods per year for a total of 13 days vacation per year. After 3 years the amount of vacation increases to 6 hrs per pay period and to 8 hrs per pay period after 15 years.