Oah... you're in C1 and you don't know about it? Well, They are substitutes for names that appeared in the previous sentence and establishing a link between the two. There are 3 main ''Pronom relatifs'': Qui (like 'who' in english'') this is used to connect a subject in a sentence. ''Tu connais la fille qui parle avec lui?'' Où is a complement of place: ''Je n'aime pas le lieu où elle habite'' Que: a complement direct object ''Le film que j'ai vu hier est très beau'' I guess I'm right. Au revoir.