When you buy your bunched or stemmed aquarium plants from Modern Aquarium, they will most likely be held by a rubber band or lead weight. You should remove the rubber band because it can pinch the stems, potentially harming that portion of the plant if it is kept in place over an extended period.
After separating the stems, remove any dead, dried, or crushed portions of the plant. Regular or aquascaping scissors are good for that but you can also try pinching the stems or leaves with your fingers if you can accomplish it without crushing the healthy portion of the plant.
Stemmed should be planted in substrate or gravel. Your gravel, or substrate, should be about two to three inches deep. This will be sufficiently deep to hold the stems down and allow the roots to fully develop.
Bunched plants look their best when planted in small and compact groups. When planting, use one or two fingers to support the stem while inserting it into the gravel. Once inserted all the way down, slowly bring your fingers up. If planting stemmed plants with your fingers proves difficult, you can use tweezers to grab and insert the plant in the gravel. Continue planting each stem separately until you're done.