The deepnet is basically any page that isn’t indexed by a search engine. websites do this so that people have to actually visit the site to find and view the content. It may require you to login or to pay but there’s nothing actually sinister about it
The darknet is a private network that you need to be invited to use by another user before you will be able to access. You would normally need to be hanging out in seedier side of the normal web to make connections with people on a darknet build up their trust and wait for an invite.