Sexual reproduction occurs in flowering plants when a male germ cell (pollen grain) is transferred to the pistil--the female reproductive organ of a flower--germinates down to the ovule which contains an egg and a double fertilization occurs. The sperm nuclei from the pollen help to not only fertilize the egg cell but the female polar bodies as well, along with another sperm nucleus form, the endosperm--a food supply for the embryo inside the seed that has formed. The offspring will be composed of a set of chromosomes from each parent and will be an individual which displays its own unique characteristics.
Apple trees can be produced sexually, as described above, or can be cloned from cuttings--a piece of a desired tree attached or graphed, to another tree. Anything that grows from the "cutting" will have the characteristics from the tree that the branch was removed from. It is a form of asexual reproduction and is a method of vegetative propagation--a desired variety of apple tree can be produced from a growing part, like the stem, of a plant.
Roses reproduce sexually as described above, as they are flowering plants. However, cuttings can be a method to propagate roses too. In this case, the cutting must include root stock from which, when placed in the soil, a new rose bush will grow.
Cabbage plants also reproduce sexually as they are angiosperms or flowering plants. Cabbage stems can be used to grow clones of the parent plant. By keeping the stem moist, it will begin to grow small roots. These can be planted and grown into new cabbage plants, exactly like the parent plant.