diff --git a/shared/challenges_markdown/three/part_one.md b/shared/challenges_markdown/three/part_one.md
index 2d04735..4b9cd6f 100644
--- a/shared/challenges_markdown/three/part_one.md
+++ b/shared/challenges_markdown/three/part_one.md
@@ -1,6 +1,31 @@
-This will be explaing the car format and will have a download link to a car file we create that they can download.
-We can create a new web handler like. /day/3/{did} and it downloads the car file.
-Inside the car export is just one record with the verficiation code
+Picking up from day 2: [records](https://atproto.com/guides/glossary#record) are kept in [repo](https://atproto.com/guides/glossary#data-repo)s on the
+[PDS](https://atproto.com/guides/glossary#pds-personal-data-server), and today we're looking at the repo!
+
+The repo (repository) is a key-value store
+
+TODO blah blah merkle tree but not getting too distracted because this is about the CAR
+
+where do CARs come in?
+
+- nice neat serialization format
+- what you get when you export your repo
+- what apps get when they sync your repo
+- what PDSs send as proof for sync.getRecord
+- what gets sent over the firehose
+
+- header with root cid
+- blocks (cid, block)
+
+- block content is dag-cbor (already covered a bit from day 2)
+- there are also MST blocks (also dag-cbor, you can ignore them if you want)
+
+OH YEAH terminology note: dag-cbor is out, i think we're all drisl now? drisl-cbor?
+
+- CIDs (ignorable)
+
+### Your CAR is ready
+
+Click the button below for your very own CAR export of an atproto repository. Search the CAR for your verification code and submit it below.
 
 <a id="download-car" href="" class="btn btn-primary btn-disabled">Loading (JS required) &hellip;</a>