It really depends on your niche, following, engagement, etc. Typically, a brand reaches out to the individual via email or direct message. If both parties think it is a good fit and the individual really likes the brand’s product, message, and values, then they come to an agreement on cost and the individual will create content in the form of a post, reel, etc. discussing why they like the brand’s product, showing how to use it, or something along those lines. I hope that helps!