Every Time Block has a Description field found with your Time Block edit view, under People and Place. You may have to scroll down to see the field while on desktop or mobile.
What it is and how to use it
A Time Block has the same framework as a Google Calendar event. Events created on your connected calendars appear in Existence and include all the information you see back in Google--including content in the description field.
The field is still there for Time Blocks first created within Existence. You can then use Descriptions as a place to include written details on why the Time Block was created. Questions you have for the upcoming call with your pet's vet, parking instructions for a job interview or a link to the website of the venue you are touring for a special event.
This makes Description part of Design. It's information you add while the time is still ahead of you.
How Description is different from a Reflection
Description and Reflection capture two different layers of the same Time Block, and the distinction comes down to timing and intent.
Description is written before or during the time — the plan, the facts, the context. It's what you know or intend going in.
Reflection is written after the time has passed. It's a micro-journal for the Time Block once it's been lived: what actually happened, how it felt, what stood out, what you want to remember. Reflection is where the experience of the time gets captured, not the plan for it.
Put simply: Description is what you expected the block to be. Reflection is what the block actually was.
Using both gives a Time Block its full dimension — the intention going in, and the lived experience coming out.