The Power Delivery Network is what provides power for all the macros in your design.
For the shuttle, OpenLANE creates a PDN that supplies the 4 rails available to the user project area:
inout vdda1, // User area 1 3.3V supply
inout vdda2, // User area 2 3.3V supply
inout vssa1, // User area 1 analog ground
inout vssa2, // User area 2 analog ground
inout vccd1, // User area 1 1.8V supply
inout vccd2, // User area 2 1.8v supply
inout vssd1, // User area 1 digital ground
inout vssd2, // User area 2 digital ground
Metal 4 is used for vertical lines that are cut for the macros, and Metal 5 routes over the top of everything.
When the metal 5 lines pass over the macro, vias are dropped to connect the macro’s internal PDN to the user project area’s PDN.
A common failure for small designs with the OpenLane tools is that there isn’t enough area for the PDN to get created. A simple fix is setting the absolute size of the die to make sure its large enough.
This is probably the best course you can get your hands on for practical stuff. If you're a hands-on guy like me it's really worth it to have the course. You can do it hand in hand with whatever theory that you're following as well. Hands-on is king for me, I mean what's the point of reading if you can't experiment - this is the mindset of an engineer.