You CAN use seeds from grocery store veggies, but those seeds are hybridized, which means you’ll get a ‘throw-back’ to the male or female species plant used to breed that particular PERFECT looking tomato or pepper in the Produce Section.
So, if you’re not picky, go for it.
If you want an EXACT variety, buy the seeds of your choice.
If you want to save seed from year to year, you need to buy ‘open pollinated’ or ‘heirloom’ varieties which will produce true from year to year.
HOWEVER, you need some protection from other nearby plants so they don’t cross-pollinate and ruin your future seed crop.
Ellendra is our resident seed-breeder/Mad Scientist; she can ‘splain more if you need more information. ;)
K - TNX :)