The Schengen area covers 26 countries, including some EU countries and some other countries and provides freedom of movement without being subject to internal border checks.
To visit countries in the Schengen area you may need a Schengen visa. The visa will allow you to stay in the Schengen area for up to 90 days in a 180-day period. The 90-day period covers all time spent in the Schengen area – including holidays and working. British citizens are covered by a Schengen visa waiver which means you do not need a visa to visit the Schengen area for up to 90 days within a 180-day period.
Keep track of how many days you have remaining on your short stay to the EU by using the helpful calculator from the European Commission linked below. Watch Sebastian Hoffman (Touring Artists) explain the 180-day rolling period from 10:38 in this webinar.