Think of waterstones like sand paper. Start with coarser grits and move to finer grits. Stop when you’ve achieved the desired finish.
For non-Japanese knives stop at 1000 grit. For Japanese go to at least 4000 grit….. But consider going higher. It is the super fine grits that give a silky smooth edge that we all love.
When choosing stones think about the size of ‘jumps’ between grits. I like only to double the grit between stones (eg. 1000 grit – 2000 grit- 4000 grit…) but one can get away with a quad jump (eg. 220/400 grit -1000 grit – 4000 grit..)