One of the most effective ways to regularly add fresh content to your site is through blogging. Shopify doesn't have the absolute best blogging system, but they do have enough features to make it work.
To create a blog:
Go to your Shopify Admin > Online Store > Blog Posts > Click the "Add blog post" button.
By default, when you create your first post, it will create a blog category/section called "News". If you would like to rename this, you can do so by clicking the "manage blogs" button above your posts.
From here, click on the name of your blog (ie. News) and it will bring up some settings where you can change the title. Once you've changed the title, on the same page, click "edit website SEO". The page will expand a bit, and under "URL and handle" highlight the end of the URL (ie. "/news/") and delete it. This will replace the "news" handle with a new handle, matching your blog's new title. By default, it will offer to redirect the old URL -- let it do this.
Need more help with this step? Check out Shopify's help docs for adding blogs by clicking here.