Stem plants often have no roots at purchase...you clip the ends back a bit to stimulate them and stick them down in the substrate, roots develop (when they get too tall just cut some off and plant, now you have more plants.
Runner plants (valisnerias, cryptocyrnes, etc) reproduce by sending out runners and new plants pop up from under the substrate along the runners, you can clip the runner and move plantlets as you wish.
Swords, etc put out long stems up into the water and plantlets develop all along it...as roots get going clip each plantlet free and plant