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.
I would recommend this course to people who don't have any awareness of open source hardware development. It can be a bit of an eye opener, a lot of people in industry have a disconnected impression of what the landscape really is.