It takes a lot of effort to properly summon an incubus or succubus. I can provide information on the method, but I think it is probably too much work for most. You will need to purchase the materials to create a proper summoning circle, seals, incense, and other related objects.
However, there may be another, easier way to cause an incubus or succubus to appear - in a half-waking state. Combining the techniques of lucid dreaming with demonolatry is a possibility. If someone wishes more information on this, message me; I am not experienced with demonolatry, so I encourage you to research it yourself as well.