Upvote:1
Type C Schengen visas are always subject to the "90/180" rule (in addition to other constraints of the visa like validity, duration...).
In any 180-day period, you can only stay 90 days in the Schengen Area. Any day you have been in the Schengen Area, even for a single minute, counts as a full day (so your arrival and departure days are both counted).
So you can for instance stay 90 days, stay out 90 days, stay 90 more days, stay out 90 days.
But you can't, for instance, stay the last 90 days of the first 6-month period, and the first 90 days of the second 6-month period, as that would make 180 consecutive days (even if you exit and re-enter Schengen).
As soon as you stay 90 days in a row, you need to stay out for at least 90 days. If you stay 60 days, then within the next 120 days (about 4 months), you can only stay 30 days. And so on.
The 90/180 rule is not reset by a new visa, so you can't either stay the last 90 days of your visa and the first 90 days of the next visa if you get one.
Also remember that on each stay you need to abide by the visa rules, on purpose, return, funds, insurance, etc. A visa never guarantees entry.