Can you specify the version of Campaign you are using?
In a general manner, you can consider a campaign to be only a hierarchy item so you can better organize your marketing activities:
Delivery templates are preset deliveries. For example, an email which already has a content, or specific properties such as the target, or the seed addresses, or anything related to the delivery properties itself. When creating a new message, you have to choose a delivery template upon which you will base your new delivery. The goal of having delivery templates is to gain some time and avoid having to edit all properties every time.
Campaign templates are one level higher in terms of hierarchy. A Campaign template can contain other objects such a deliveries or workflows for example. When creating a new campaign, you can reuse a campaign template to already have several deliveries or workflows created inside.
Hope this helps,
Let me know what your version of Campaign is (Standard or Classic) and I'll be able to give you more details and link some relevant resources if you need.
Case 1: I usually send different newsletters to my customers, so my emails all have the same background, logo, links to social medias, only the core content in the middle of the email is updated. I can use a delivery template to have all these common elements already defined in my email. When creating a new email based on this delivery template, I will just have to fill the content that needs to change, all the rest will already be defined in the template.
Case 2: I have a "Christmas" campaign which contains various deliveries, for example one to give a discount for early birds in October, and another delivery to remind people that if they want to receive their purchases before Christmas, they need to order before 10 december. Here, my campaign contains 2 objects. Next year, I want to do another christmas campaign, and since it worked well last year, I will do something similar. So if I have a campaign templates that contains those 2 elements already, I'll gain time and won't have to create everything from scratch all over again. Of course, you can add some complexity by adding more deliveries to the campaign.
In short, a delivery template is a template for 1 delivery, while a campaign template is a template for several objects like deliveries or workflows, all together.