You can eat the fruit, spit out the seeds, let them dry. Plant in a pot with mosit soil, will sprout in ten days. Long time for fruit, however.

Or ask for a pad or two. Let the pads callous, then in the spring plant in a suny location, water once, let nature do the rest.

When I lived in Las Vegas, I was a member of the Cactus and Succulent Society of Southern Nevada and when I was at one of their sales, I picked up a pickly pear pad and a tiny barrel cactus. Planted in my yard, watered once, and years later the Opuntia grew into a tree 7 feet high. You would of course, need a male and female plant, I presume for fruit.

Sagebrush

Opuntias are monoecious (having both female and male reproductive structures) and self-fertile (at least all the common ones I know of), so one plant can produce fruit all on its own.

I wouldn't bother planting seeds if your neighbor is willing to give you cuttings. Much, much faster route to a big, fruit producing plant. Just make sure where you plant it has adequate drainage and sun exposure.