Teachers: Teachers teach you something. They can teach anything but it usually is occult knowledge or a lesson you need to learn.
Protectors: Protectors are just that, protectors. They watch over you in everyway. Physically, astrally, etc. However, sometimes they cannot protect you either because of your own choices resulted in harm, a lesson, test, etc.
Messengers: These are not quite as common as Guides, Teachers and Protectors. These are usually relegated to those who have a specific Spiritual Job/Mission that they would need a messenger for. Messengers are kind of like gophers. They retrieve information, give messages, etc.
The above Spiritual Helpers are usually evolved humans who have no need to return to the physical, but are not yet done learning and growing and the above jobs help them learn more etc. The above come and go as they learn and grow and are usually replaced by others. Sometimes you have more then one guide and/or teacher etc. It all depends.
The following is an exercise designed for you to meet your Guide or Teacher. Messengers you wouldn't really need to do this with but you could. As for protectors, they usually aren't to talkative.
What you need: A quiet place to meditate.
What to do: Relax. Decide who it is you wish to contact through this meditation (guide or teacher). Take a few deep, cleansing, relaxing breaths. Visualize your surroundings change into that of a pleasant scene. It can be any scene you like. It can be a grassy meadow, a beach, forest glade, cottage or anything else you can think of that conveys peace and tranquility to you. Walk around this place and familiarize yourself with it. After a few minutes you will see a figure in the distance. They are walking directly toward you. This is your Guide or Teacher. When they get close enough to see them clearly, note how they look. Dark hair? Light hair? Fair skin? Dark skin? What kind of clothes are they wearing? etc. Greet them and ask them for a name. Remember it and then invite them to sit with you or just speak to them standing. Ask them what their purpose is, what they can teach you, etc. Ask them anything you would like. This can be your meeting place where you can commune with your Guide/Teacher in peace and serenity. When you are done speaking with them (and they done with you) then thank them and let your surroundings fade to black. Clear your mind then open your eyes.