Questions & Answers about Вчера мы были в лесу и катались там на лыжах.
Why do we use the multidirectional verb катались here instead of a unidirectional one?
In this sentence, the action of skiing is done for pleasure around the forest, moving in various directions. Because it is not a single, continuous trip from point A to point B, the multidirectional verb кататься is required.
I thought кататься meant 'to ride' or 'to roll'. Why does it mean 'to ski' here?
In Russian, to express taking a ride or doing sports on equipment, you use кататься на followed by the prepositional case of the vehicle or equipment. So кататься на лыжах literally translates to 'riding on skis', which is the standard way to say 'to ski'.
Why is the prepositional form в лесу and not в лесе?
The noun лес is one of a small group of short masculine nouns that take a special locative ending -у (always stressed) when used with в or на to indicate physical location. The regular prepositional ending -е is only used when talking about the forest, like in о лесе (about the forest).
Why does катались end in -сь instead of the full reflexive ending -ся?
The reflexive suffix changes depending on the letter immediately before it. Because the plural past tense ending -ли ends in a vowel, the suffix shrinks to -сь. You only use -ся after consonants.