@simplifiedimpact01 

1. For Abandoned Cart, Klaviyo tracks when someone Started Checkout and tracks when someone Placed Order.  If you’re using the standard Abandoned Cart Flow in Klaviyo, Klaviyo is checking if someone who started a Checkout but does not complete an order within your time delay.  So the Cart Abandonment, is more precisely defined as a Checkout Abandonment.  There are work arounds for a true “Cart Abandonment” - you can read up on that method here: How to Create a Custom "Added to Cart" Event for Shopify
2. Klaviyo tracks all Placed Orders, Ordered Product, and Fulfilled Orders through direct integration with the most popular ecommerce platforms. 
3. Not sure what you mean by “link a specific action” - but you can see a list of all the events Klaviyo track in your Klaviyo → Analytics (Sidebar) → Metrics page.  Any other events you can add programmatically via the Klaviyo API where you can send in any events (and it’s associated data).  See this Documentation for custom events: Track and Identify API Reference and the Developers section in this community.
4. Here’s a good intro to Custom Properties in Klaviyo: Guide to Properties. You can add unlimited custom fields (Custom Properties) into Klaviyo through any of these methods:
   1. Manually adding them in a Profile
   2. Adding them via a Klaviyo Signup Form
   3. Adding them via the Subscribe or Manage Preferences Page
   4. Adding them via a 3rd Party Integration (or Tool)
   5. Adding/Updating them via Links in your Email
   6. Adding/Updating them from a Update Profile Action in a Flow
   7. Bulk Importing them into Klaviyo via a CSV Upload
   8. Programmatically via the Klaviyo API

Hope this helps!

Hi @simplifiedimpact01,

To expand on @retention’s great answers, I wanted to point out that for 3, “Can you also link a specific action to a list such as checkout that Klaviyo can add automatically in the list?” rather than a list, you can build a segment where someone does x action and is added to the segment. You can then use that segment for a variety of uses: to trigger a flow, target a campaign, target a form on your website, create a custom Facebook audience, or for analytics purposes.

Hope this helps!