When using the passé composé with verbs that involve getting hurt, like se blesser, se couper, and se brûler, you change the ending of the verbs a little bit depending on the gender and number of the person getting hurt.
Nous nous sommes brûlés.
We got burned.
Elle s’est blessée.
She got hurt.
But if you know exactly which body part was affected, then the gender and number will not have any effect on the verb.
Elle s’est brûlé la main.
She burned her hand.
Ils se sont coupé les cheveux.
They cut their hair.
When using names of body parts in a sentence, there is a difference between English and French. In English we use words like his, her, our, or their, but in French you use le, la, and les.
Il s’est cassé la jambe.
He broke his leg.
Tu t’es brossé les cheveux.
You brushed your hair.
Some verbs can be used both with and without se, like couper and se couper, blesser and se blesser, and tuer and se tuer.
Elle coupe la viande.
She cuts the meat.
Elle s’est coupée.
She cut herself.