The penis should be erect (hard) before putting on a condom. Then begin by placing a rolled up condom on the tip.
Squeeze out the air from the end of the condom (to make room for any cum), and unroll the condom to the base of the penis.
Use plenty of water-based lubricant on the outside of the condom.
After cumming, hold onto the base of the condom firmly (to stop any cum leaking), then pull out. Use each condom only once.
Dispose of the condom in a waste bin. Do not flush it down the toilet.