There is also a powerful search that you can use to find things.
The first item on the page is an ensemble of streak indicators that give you a brief overview of the last 7 days. They visualize on which days you have written entries, if those entries have 3 or more bullets (that should be the minimum), and whether or not they include Dreams and/or Highlights (in the future they might also indicate items from other modules).
Streak is useful for quick review, pointing out when you are missing an entry or when you have forgotten to mark a highlight, etc.
You can click on an indicator to add an entry for a day or open it if it already has one.
The timeline allows you to browse back in time and look at your previous entries. In practice, this works only well for the last couple of days/weeks. To go further back in time, have a look at the calendar feature.
Some useful options (see Settings):
Shows the running number of an entry in its header, aka. the how manyeth entry you are looking at.
Use these options to truncate long dreams and bullets after 5 lines in the timeline view (doesn't apply to Entry details).
On the top right of the Journal page, you'll find a convenient pop-up calendar that you can use to jump to specific dates or to create entries for dates that do not have one yet.