Some German verbs need a small extra pronoun called a reflexive pronoun (Reflexivpronomen) to show that the subject performs the action on or for themselves: sich waschen literally means "to wash oneself." You need this construction daily — for talking about morning routines (getting washed, getting dressed), emotions (getting happy, getting angry), and plenty of other situations that have no obviously "reflexive" meaning in translation at all.
The reflexive pronoun sich isn't fixed — it changes with the subject just like the other pronouns you already know: ich → mich, du → dich, er/sie/es → sich, wir → uns, ihr → euch, sie/Sie → sich. Notice that sich only appears with third person singular and the formal plural; every other person reuses the same accusative pronouns — mich, dich, uns, euch — you already learned in A1, which makes them easier to remember than they might seem.
In terms of word order, the reflexive pronoun comes right after the conjugated verb in a main clause: Ich wasche mich jeden Morgen. In a question, the verb and subject invert as usual, but the pronoun still follows the subject: Wäschst du dich?
One important detail: most reflexive verbs use the pronoun in the Akkusativ, but some use it in the Dativ when there's another direct object in the same sentence, such as a body part: Ich wasche mir die Hände — here mir is dative because die Hände is the real direct object.
Here's where German diverges most from many other languages: a large number of German reflexive verbs don't translate as reflexive at all. For example, sich freuen simply means "to be happy," not "to make oneself happy"; sich interessieren für means "to be interested in"; sich beeilen means "to hurry." Many languages express these with ordinary verbs and no equivalent of "oneself," while in German sich is an essential, non-optional part of the verb — dropping it can change the meaning entirely or make the sentence ungrammatical.
The most common mistake is forgetting sich altogether with these non-obviously-reflexive verbs, since the meaning doesn't intuitively call for "oneself." That produces incorrect sentences like Ich interessiere für Fußball instead of the correct Ich interessiere mich für Fußball. The practical fix: from the very first day you learn a reflexive verb, memorize it together with sich as one inseparable unit, the same way you memorize a noun together with its article.