Welcome to the SeeMeCNC Community

Just needing a clarification. I've got the USB cord that I'd used to connect the rostock to my computer connected to the raspi unit instead of my computer.

I've got the sd card imaged with Astrobox.

Now, to get things booted up correctly, do I use the mini-sd card portion and plug it directly into the raspi before startup, or do I leave the mini-sd card in the sd adapter and plug that into the slot on the left side of the lcd controller?

You plug the SD Card into the raspberry pi because it is the code for the Raspberry pi and OctiPrint software. The printer SD slot is for GCode files to be printed. However it is not needed if you only use the OctoPI to control the printer.

Dale