Since you are working in the round you work all the charts from right to left on every round. Start at the bottom of each chart and work up just as you'd knit.
This is what your pattern says once you have your 100 sts and are ready to begin the charts:
P 3, M.2, P 6, M.3, P 6, M.2, P 6, M.2, P 6, M.3, P 6, M.2, P 3.
I took out all the numbers that refer to the other sizes. When I work Drops patters I like to copy and paste the pattern in a Word document and edit out the numbers that don't apply to my size. It really cuts down on confusion.
So here is what you do on this first round:
P3, then work right to left across the bottom row of the M.2 chart (it is over 6 sts), then P6, work right to left across the 20 sts on the bottom row of the M.3 chart, P6, do the same 6 sts of row 1 of chart M.2, P6, do the 6 sts of row 1 of M.2 again, P6, work right to left over the 20 sts of the first row of M.3 again, P6, row 1 of M.2 again, P3.
So you P3, CH (chart)6, P6, CH20, P6, CH6, P6, CH6, P6, CH20, P6, CH6, P3. 9X6=54+40 (for the 2 of CHM.3)+6 (for the 3 at each end). 54+40+6=100
The next round will be just the same as far as the stitches between the charts, but you will work row 2 of each chart (next to bottom row) right to left. Keep working that way up the chart, reading right to left, and putting the purls between.