An Account will generally be used for a company name.

For example, a company has their holiday party at your venue every year. You will want to keep that information together. A longstanding, recurring Account may have multiple Contacts. The Contacts in this case being who is the Account representative you are working with.

Contacts don't necessarily have Accounts.

If you are hosting someone's wedding, you won't often need an Account associated with them. Even if they book multiple Events or return throughout the years, all of this can be stored under their Contact with no need for an Account, because the person you are dealing with (the Contact) is unlikely to change.