Protein Powder
Protein powder is really just convenient food. If you train, or simply struggle to hit your protein from meals, a shake is a quick, cheap way to top up. Whey is the classic and mixes well; plant blends have come a long way for anyone avoiding dairy. Ignore the flashiest tubs and look at protein per serving, taste (you have to actually drink it) and price per kilo.
Common questions
Do I need protein powder?
Only if you are short on protein from food, which is common if you train hard or eat lightly. It is a supplement to a good diet, not a magic muscle powder. Whole foods first, powder to fill the gap.
Whey or plant protein?
Whey is cheap, complete and mixes smoothly. Plant blends (pea, soy, rice) are the pick if you avoid dairy and have improved a lot on taste. Both do the job; choose on diet and preference.