The term Spirit Guide generally makes reference to one or more entities who watch, teach, heal, and help you on your physical journey into spiritual awareness. They are above in higher frequency, while you experience the physical below.
Communication is generally telepathic, clairaudience, with archetypes and visual imagery, clairvoyance, observed during meditation, dream time, or just learning how to focus, look and listen to messages received. Some people call this method of connection, channeling. The more you practice, the easier it gets.
The number of spirit guides one has various within that person's experiences. The strongest connection is with the aspect of your soul referred to as your Twin Flame - dual aspects of a soul, above and below, programmed to seek reunion to feel complete, oneness. The twin soul reference to 'spirit guide' remains with you until you rejoin when leaving the physical body.
Spirit guides can go by many names. Often they connect with more than one people at a time, using identities that are comfortable to those they communicate with.
Spirit guides may be viewed as any type of non-physical, perhaps an alien ... however they are perceived.
Each guide generally comes to you for a specific purpose - creative abilities, healing issues, spiritual development, etc. A guide can save you during an accident, by entering your body or stopping time.