Зворотні дієслова на -ся

Many Russian verbs carry a small tail, -ся. It comes from an old word for "oneself", and in some verbs it still means exactly that. In many others it simply belongs to the verb, and English has no equivalent at all.

-ся or -сь?

In the infinitive and the conjugated forms, the tail is -ся after a consonant (or ь) and -сь after a vowel. It sits at the very end of the word, after the ending:

In the past tense: он учи́лся but она учи́лась, они учи́лись. In speech, -тся and -ться both sound like [tsa]: нра́вится and нра́виться are pronounced alike, a favourite source of spelling mistakes even for Russians.

What -ся does

• Action on yourself: мы́ться (wash oneself), одева́ться (get dressed). English drops "myself": "I wash, I get dressed". Russian still needs the tail: Я умыва́юсь и одева́юсь. Without it, Я одева́ю leaves your listener waiting for an object: dressing whom?
• Each other: встреча́ться (meet), целова́ться (kiss): Мы встреча́емся у метро́ «Пу́шкинская». - "We're meeting by Pushkinskaya metro station."
• Passive, about things: Мост стро́ится - "The bridge is being built."
• Verbs that come with -ся: смея́ться (laugh), боя́ться (be afraid), нра́виться (be pleasing). Here the tail has no separate meaning; learn it as part of the word.

Two traps for English speakers

Нра́виться turns "I like" inside out: the thing you like is the subject, and you are in the dative. Мне нра́вится Каза́нь is literally "Kazan is pleasing to me".

English "study" splits in two. Учи́ться means to be a student somewhere: Я учу́сь в университе́те. To study a subject, use изуча́ть with a direct object: Я изуча́ю ру́сский язы́к. Saying *Я учу́сь ру́сский язы́к is one of the most frequent errors in beginner Russian, because verbs in -ся do not take a direct object in the accusative in standard Russian.