When - July to about now. Ideally mid July.

How. Cut off a firm but not woody stem about 4 to 6 inches long.. preferably a non flowering stem but this isn't always possible .(If it has flowers remove them)

Cut the stem immediately below a leaf joint. remove the leaves from the next one or two leaf joints up.Dip the cut end of the cutting in rooting compound( not strictly necessary but it will improve the percentage that take) Put the cutting in a mixture of 3 parts potting compost to one part horticultural sand. Water well and thereafter keep in a shady spot outdoors or preferably in a shaded coldframe. Rooting should occur in 3-5 weeks. Some people recommend putting the cutting in its pot in a plastic bag. I find they often rot off doing it that way. I take hundreds of hardy fuchsia cuttings a year by the method I've described.

Even if the fuchsia is a hardy species I'd recommend over wintering indoors for the first year and plant out after all frosts are over usually mid to late may in mid latitud UK

I've just notified you're from America Liz so the "when" part of my answer won't be appropriate unless you live in a State which has weather similar to mid latitude UK.