welcome to GoY.
if you find a shoot with out a flowering stem pull the shhot down wards so it tears off. it will a jagged 'spur' of torn stem. this is called a heel cutting.
you now have a choice
1. put the cutting into a glass of water and wait until roots form 2-4 weeks usually, then pot the cutting up into good quality compost.

2. pull off half the lower leaves. pop the cutting[s] down the side of a pot filled with compost. firm the compost against the cutting and the pot side. water the pot and keep barely damp. again roots should form in 2-4 weeks.

the cuttings can be kept on a window cill or in a greenhouse if you have one.

I often find suitable cutting material in bouquets of flowers/carnations/pinks. I have had some lovely freebies this way.

I've done the same thing with bought carnations/pinks. Sometimes all I've done is stick a cutting in the ground and it's grown nicely but it all does depend on keeping it moist and not letting it dry out.