Flat pedals are what most bikes ship with — you place your foot on top, no special shoes required, and you can put a foot down instantly at a signal or when balance wobbles. For commuting, errands, and casual riding, this simplicity is a genuine advantage, not a compromise.
Clipless pedals mechanically lock a special cleat on the shoe to the pedal, letting you pull up as well as push down through the pedal stroke — more efficient for sustained effort like long-distance or competitive riding. The trade-off is a learning curve (a stopped rider forgetting to unclip is a rite of passage) and the need for specific shoes.
For the vast majority of everyday cycling — commuting, errands, weekend rides — flat pedals are the simpler, more practical choice. Clipless is worth considering only once riding becomes frequent, sustained, and performance-focused.