Everything you need can be done on the website. You can write and edit posts, manage users, and customize your site without any special technical knowledge.
Haven is about sharing privately with friends and family. There is no option to make your blog public to the world. You get to create an account for anyone you want to have access. When they connect to your site, they use https encryption between their web browser and your server. That means nobody can intercept and read your posts. Since you create accounts for people, there is no place for spammers or internet bots try creating accounts.
If you want a public blog to build a base of followers, or promote a product, or try to profit from your blog—this isn't the right service for you. I suggest you use Wordpress instead.
Haven uses Markdown for writing posts. This gives you the full expressivity of rich HTML without needing to know any HTML. There is a live preview of your post as you write it so you know how it will render. There is also extra functionality for uploading images. You upload an image and the server will automatically add the markdown to reference that image.
The pages your visitors see are very compact, so they load fast everywhere. There is no advertising or web tracking so the code that makes pages big and slow don't get loaded. Haven also automatically compresses your images so they still look great but take much less time to download. It saves the original uploaded image so someone can click an image and see the original full-resolution image you uploaded.
With the AWS deployment scripts or the Haven hosting service you get automatic nightly backups of your blog. If something ever goes wrong, those backups mean your site is restored without losing everything you've shared.
Haven is a place for you to express yourself. It comes with CSS—special styling that controls how the page looks—and it also lets you customize that CSS from within the site. The default styling is simple and works great for desktop and mobile users. Customizing the CSS lets you control everything, from the colors to the layout. Note that CSS takes some technical knowledge, but this gives you full control instead of just the ability to pick from a few themes.
Users can be subscribers, or publishers. With publishers multiple people can post to the blog without sharing passwords. This could be multiple parents posting pictures of their kids, multiple leaders of a community group, or even multiple students as part of a school project.
When many people run their own website, it can be tedious to visit everyone's page to look for updates. The internet solved this problem a long time ago with a tool called RSS. Readers for RSS aren't as common as they once were, but Haven includes private RSS access with a unique secure link for each user.