The purpose of summoning these beings is to either request them to aid you in some way, in the case of angels, or to compel them to assist you in whatever area they have authority in, in the case of demons.
How does this apply to God or other deities? Well, first, you don't summon gods. They tend to not like to be ordered around. But you can call upon them to aid or assist you. As far as the Judeo-Christian God, It is well documented in religious texts that Solomon was given the knowledge of commanding demons, and Jesus claimed to be, at one point, more powerful than Solomon. If you are interested in that aspect, the Key of Solomon and the books associated with it are of particular interest. Start with the Grimoire of Armandel.
How one commands them is usually by invoking those beings who rule over the entity you are working with. Which, in theory, means you have established a working relationship with these ruling entities. It also helps if you have experience with assuming godforms so that you can command not through your authority but through the authority of that ruling entity. You should be careful in trying this however. If you assume the wrong godform it can have some serious psychological effects.