Summoning of an energy concentration is used for several different purposes. A magickian may call an entity to begin spirit communication, for protection, to help with another casting, or any of several other reasons. As with any spiritual magick care should be taken to guard against an incorrect summoning.
When a spirit is summoned it may appear physically, in the mind’s eye, or be invisible, but audible (as in the movie "Ghost"). In any case communication , depending on the casting intent, should be possible with the energy concentration. This is usually achieved verbally (by talking out loud).
If the casting was done correctly and nothing seems to have happened then the magickian’s energy vibrations are too low to interact with the summoned entity. If this is the case a reverse should immediately be done and the magician should work to raise their energy to another level before attempting the casting again.