This is the 10456th most frequent Spanish word.
contarle
"To tell [someone]."
Here, 'contarle' is used in the sense of narrating or relaying information to the third person 'your mother', where '-le' indicates the indirect object.
No olvides contarle a tu madre sobre el evento.
Don't forget to tell your mother about the event.
In this instance, 'contarle' expresses the desire to communicate ideas to the teacher, with '-le' marking the teacher as the recipient of the action.
Quiero contarle mis ideas al profesor.
I want to tell my ideas to the teacher.
In this example, 'contarle' conveys the intention to report or narrate what happened to someone, with '-le' indicating the recipient of the narration.