Display rules can be set for any block, they determine the circumstances under which a block will appear in checkout.
If all the conditions required are met, then the block will be eligible to show. If there is more than one block eligible to show for the block then one random block from the list of eligible block will show. If you want to fix the block to show one specific block you can set that within the block setting within the Checkout editor How to add a specific block to checkout.
The component will be eligible to show for all checkouts.
This option is the most flexible of the listed options as it allows you to combine any combination of rules.
Using the AND operator will make the rules behave as in Show when all rules pass and using the OR operator will make rules behave as in Show when any rules pass. The main difference being this option allows for the mixing of AND and OR to make for even more specific targeting.