Schengen / the Schengen area
The Schengen area comprises 27 European countries. There is normally no passport control on the borders between these countries. If you have a valid visa or residence permit in one of these countries, you can also visit the other Schengen countries.
The Schengen area consists of
Belgium, Denmark, Estonia, Finland, France, Greece, Iceland, Italy, Latvia, Liechtenstein, Lithuania, Luxembourg, Malta, Monaco, The Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Switzerland, Sweden, the Czech Republic, Germany, Hungary and Austria.
Crossing borders in the Schengen area
When you enter and leave the Schengen area, you must show your passport.
If you are a subject to a prohibition against entry, you will not be allowed to enter Schengen, for example if you have been expelled from another Schengen country because you have committed a crime.
Visitor's visa / Schengen visa
If you have a valid visitor's visa in one of the Schengen countries, you can also visit the other Schengen countries.
The visa states how many times you can enter Schengen (one, two or more entries).
If your visa is only valid for one entry, you have to remember that if you leave Schengen, for example to go to the UK, Ireland, Russia or Turkey, you cannot re-enter Schengen without being granted a new visa. It is therefore important that you state in your application for a visitor's visa how many times you will be travelling in and out of Schengen during your visit.
http://ec.europa.eu/dgs/home-affairs/what-we-do/policies/borders-and-visas/border-crossing/schengen_calculator_en.html
You can stay in ... and the rest of the Schengen area for up to 90 days during a period of 180 days.
You can divide the 90 days over several visits and travel freely in and out of ....
If you have been in the Schengen area in the last 90 days, you must check when it is possible for you to re-enter, and how many days you can stay in Schengen. Please use the visa calculator to check this (ec.europa.eu)