Situated in the western parts of The Netherlands, Rotterdam is the second largest city in the country with over 1.3 million people living in the metropolitan area. Rotterdam is also famous for its port, which is the largest in all of Europe and was the busiest until 2004. The city of Rotterdam is a common place for backpackers and travelers to visit while traveling Europe, and is very well known for it's architecture and culture.
Rotterdam is served by Rotterdam/The Hague Airport (RTM), although most people (especially travelers) reach the city by trains or buses. If you do fly in, you can take the public transport to the city (a bus). Eurolines is probably the best bus option if you are traveling around The Netherlands and wish to go to Rotterdam.
Hostels in Rotterdam are of great value and mostly situated in the city central, so you won't be far away from most sightseeing spots. A dorm bed will set you back about 20 euros. Double / twin rooms are a bit more. The Rotterdam hostels are generally close to the city's public transport which is very efficient and a great option to get around the city. However, like in most cities in The Netherlands, bikes are your best bet (just be careful!).
While you're staying in a Rotterdam hostel, it is a good idea to see the world-famous port and the Maritime Museum. The city is packed with many other museums which are very well worth the time if you're interested in the subject. Rotterdam is also known for its architecture which makes the city very scenic if you go for a walk.