Prague is well connected to the rest of Europe. It is easy to get in by plane, by train, by car or by bus. However, the ring road around Prague is not complete. This leads to traffic jams during rush hour.
Prague has one airport called Ruzyně International Airport. It is about 20 km out of the city. A lot of flights are operated on this airport, so it is easy to get in Prague from many other European airports. The airport is connected to the city center by buses and by taxis. Trips take half an hour. Regular buses are the cheapest, one ride is around €1. There is a special and faster Airport Express bus, that costs around €2. Other private companies may operate buses or shuttles from the airport to the city center. A taxi ride is about €30.
Getting in Prague by car is easy, since there are motorways coming from all major directions. It can be a nightmare to pass through Prague though, since the city has no ring road. You will get directly through the city, so you will experience all the traffic jams at rush hours. Avoid these hours in order to save time. If you come from the Eastern part of Europe, you will likely use D1 that passes through Brno and arrives in Prague. Other motorways connect Prague to Germany. D5 gets you in Nürnberg through Plzeň and D8 gets you in Dresden.
Prague has one international train station called Praha hlavní nádraží. There are good links by rail from other European countries. From this central station, you can get around Prague by underground. You should be very careful if you take a taxi from this train station, there are a some illegal taxis that charge you way too much.
International buses use the Florenc station. You can take the underground from here to reach other parts of the city.