The 66-18 is an oscillating hook, drop in bobbin machine that uses Class 66 bobbins and 15x1 needles.
The needles go in flat to the right and it threads left to right.
It has a stitch control lever with a back tack feature.
It uses low shank feet and attachments.
They use the standard Singer motors that are not the highest amp motors you'll find, but they are strong machines so don't underestimate them.
They sew very nicely.
Easy to clean and maintain, parts are pretty common.
To clean the crinkle finish use cotton balls and oil. You'll be surprised at how well that cleans them up.
Anything else just ask.
Joe