I highly recommend writing your own toy version of LISP in whatever language you already know. Just enough to get the basic eval loop working (+ macros if you feel brave).
It is fun and IMHO the best way to learn LISP.
If you get stuck read through one of the many examples online and then try again without looking at those examples.
I just wish many of the software projects the code in the book depends on had been maintained. Portable Aserve and the Shoutcast server are two examples that come to mind off the top of my head, and of course the Lisp in a Box environment is long gone, and the replacements, like Portacle, are also getting left behind.
2022 https://news.ycombinator.com/item?id=33162318
https://news.ycombinator.com/item?id=29850703
2018 https://news.ycombinator.com/item?id=17644067
2016 https://news.ycombinator.com/item?id=13096576