You made a master by handwriting or typing on a special combination of paper types. By the way, I do mean typing, not word processing. We were using old-style typewriters and any mistake was a real pain to correct. Then, you removed a sheet from the master that had your original turned into purple on the paper. You attached that sheet to the drum on the mimeograph machine, loaded in a stack of blank paper, and started turning the handle. If your school had a fancier machine, it turned itself with a motor. As the drum made contact with each sheet of blank paper being fed through, the machine transferred an image to the paper. A little of your master wore off with each sheet; so, masters wouldn't make copies forever. The smell came from the fluid in that gallon container in the picture, and you could smell it far down the hall whenever someone was making copies. Here's a YouTube video showing a mimeograph machine in action. They were loud!
Do I miss mimeographs? No, not at all. I don't even miss photocopiers now that I've moved to almost-paperless teaching. Mimeographs do remind me, though, of a very different day of teaching the first time I was in the classroom. No photocopiers, no word processors, no spreadsheets, no cell phones, and no Internet! The last one seems to be the one that amazes my Net Generation students the most. We taught without any Internet support. All we had where our textbooks, the supplemental materials that came with them, and any resources we had collected on our shelves or in our filing cabinets. We were all little teaching islands in our own classrooms.