Surfing is a very popular activity in Rio. Both for Cariocas as well as for Gringos! What else could you expect of a place with so many beaches?
Arpoador is the most popular in-town surf spot and it is illuminated at night allowing people to surf into the late hours. The popularity however means that it gets crowded and does not make it the best spot for beginners.
Prainha is another well known surf location, it has high quality waves and it can get crowded. So also here you need to be careful if you are a beginner.
Barra and Recreio are the best places for beginners. The beach goes as far as the eye can see which means you will able to find some free space.
If you want to buy surf equipment or accessories a good place to go is the Galeria River at Rua Francisco Otaviano 67 in Arpoador. Here you can find several shops focused on surfing, skateboarding etc. Most people working there practice the sports themselves and can therefore also give valuable tips.