After clicking "Manage feeds" you can see the announcement's admins page, in which you can manage Feeds and Announcements.
Now from the left bar (FEEDS) choose your feed.
Then on the other side from the right bar (ANNOUNCEMENTS) find and click the "+ Add New Announcement" button.
After that, a new window will show up, in which you can create an Announcement in 3 steps.
Step 1 - Select Type
At this point, you can specify a type (Single Issue, Multiple Issue, Simple Text or Confluence Announcement).
Step 2 - Define
This part is responsible for:
- Announcement name & description, Issue, JQL filter or Confluence link
- Start and End date - when the announcement will start and end be visible to users
- Redirect URLs - on which page users will be redirected after clicking Approve, Reject or Dismiss button
Note: You can leave this field empty, and then users will stay in Jira.
Step 3 - Preview
Here you can see what your announcement will look like. If it looks different than you want you can click the Previous button or check your Feed's configuration.