In his conversation with Lionel, Lahlou describes his daughters' success in school and sports in an interesting way. He uses the verb assurer:
Les deux grandes franchement, elles assurent. Elles assurent super bien à l'école, au sport.
The two older girls, frankly, they're doing great. They're doing really well in school, in sports.
Captions 82-83, Lionel & Lahlou Être musulman - Part 2Play Caption
Elles assurent is a familiar way of saying "they're doing great," "they're doing a great job." Lahlou also could have used the preposition en to specify what the girls are succeeding in: elles assurent en maths (they're good at math), elles assurent en natation (they're good at swimming).
More often, assurer means "to assure" or "ensure," or, when reflexive, "to make sure"/"to check":
Je vous assure qu'elle est là.
I assure you that it's there.Play Caption
Mais on doit s'assurer que le pneu est bien assis sur la jante et ne pas trop gonfler.
But we have to make sure/check that the tire is well-seated on the rim and that we don't inflate too much.
Caption 19, Sports Shop La mécanique d'un véloPlay Caption
Assurer has a few other meanings as well. It can mean "to secure" or "achieve":
Ses affiches et ses tableaux ont permis au Moulin Rouge d'assurer une notoriété rapide et internationale.
His posters and his paintings allowed the Moulin Rouge to achieve rapid international notoriety.
Captions 19-21, Amal et Caroline Moulin RougePlay Caption
Il est difficile d'assurer un emploi en ce moment.
It's hard to secure a job these days.
It can mean "to take care of," "handle," or "deal with":
Je dois assurer l'école.
I have to take care of the school.
Caption 13, Les zooriginaux 3 Qui suis-je? - Part 2Play Caption
La brigade des pompiers assure l'extinction des incendies.
The fire department takes care of putting out fires.
Or it can mean "to insure," as in "to provide insurance coverage":
Notre maison est assurée.
Our house is insured.
Likewise, its noun form assurance can either mean "insurance" or "assurance," or more precisely, "self-assurance," "confidence," "certainty":
Le stress au travail a en effet un coût, humain bien sûr, et économique pour l'assurance maladie: près de cinquante milliards d'euros.
Stress at work does indeed have a cost, a human one of course, and an economic one for national health insurance: close to fifty billion euros.
Captions 57-58, Le Journal Le stress au travailPlay Caption
Il faut parler avec assurance pour convaincre les gens.
You have to speak with self-assurance/confidently in order to convince people.
So whether you're assuring, ensuring, making sure, or insuring, assurer is the verb to use. You can find even more ways of using it here.