Hi Terri,
Select your cuttings from healthy disease-free plants. Each cutting should be about 3 inches long, although this will vary with the type of pelargonium being propagated.
Make a clean cut just below a leaf joint (node); remove most of the leaves from the stem plus the stipules and any flower buds. You should now have a cutting with the terminal leaves and perhaps one or at most two leaves at the top of the stem. Insert this cutting into your cube of oasis OR better still into a small pot of compost/vermiculite 50:50, water and allow to drain thoroughly. Do not use rooting compounds or tent the cuttings place in good light, not direct sunlight in a warm room and they will root in a few weeks.