The simple future tense in French is used to express ‘I will + verb’ in English. Nous mangerons au restaurant si tu veux. – We will eat in the restaurant if you want. Elle jouera au foot le week-end ...
Modal verbs, which express a likelihood, ability, permission, request, order etc., usually help main verbs to state the future. It is the reason they are categorised as auxiliary verbs in the context.