What sort of stem cutting? There are hardwood, softwood, semi-hardwood (half ripe) and so on.
In general terms you remove from one half to one third of the leaves on the lower part of the stem and insert it into the compost up to the first leaves which are left.
Not everything will come from cuttings, and the key to successful rooting is keeping the cutting humid and not letting it dry out, but at the same time avoiding rotting. Covering the cuttings with a plastic bag is the easiest way of maintaining humidity. Keep them out of direct sunlight, but in a light place. And use a gritty or well drained compost: 50/50 seed compost and vermiculite or perlite is quite good.
Certain things don't like to be covered with a bag, pelargoniums, for example, which will root readily without being kept so humid.