Your domain name makes it easy for people find your website, without it people would need to memorise a complex number (akin to memorising a telephone number) to find your website.
Your hosting provider makes your website available to the public, without it your website won’t be online for people to visit.
Without both, your customers won’t be able to find your website. Imagine having a bricks-and-mortar business, but without a physical store or an address for people to find you.