Great article in MagPi 69 on getting into 3D Printing and using the Raspberry Pi with OctoPrint software to run the printer.
The article does gloss over some important details in getting OctoPrint up and running. If you need help I suggest visiting the OctoPrint web site go to the downloads page to find the current OctoPi image, and scroll down a bit for installation instructions, including text description and a video.
Visit this YouTube page for a very good series of OctoPrint Tutorial Videos by Joe Mike Terannela, including basic initial set up, plus separate videos on a number of advanced topics.
If you need further assistance, visit the official OctoPrint support web site. Check out the help and FAQ section. Odds are if you are having a problem, someone has already worked through it.
Here is an OctoPrint FaceBook group which may also be helpful.
NOTE on Raspberry Pi 3B+: The current OctoPi image as of the time of this writing is 0.14. This version does not work with the new Raspberry PI 3B+. If the stable version of OctoPi 0.15 is available, you should use that - it will be linked on the OctoPrint website download page noted above. At the time of this writing, an OctoPi 0.15 release candidate is being tested. This does work with the Pi 3B+, but has not yet been fully tested and debugged. Initial reports are that people are running it successfully. OctoPi 0.15 does change how you set up a WiFi connection: You'll need to find the octopi-wpa-supplicant.txt file in the boot directory and follow the directions there, rather than the octopi-network.txt file mentioned in the article.