Been reading through some of the threads here. I don't know much about spirits, nor have any special talents. I'm wondering who are usually our spirit guides? Why have they been chosen to be our guides?

Spirit guides have chosen to take on this job.  Some wish to be of service.  Some grow through their service to others (us).  

They are all here to do the best they can in aiding our journey of life.  They have lived an earth life before and know the challenges we face.  They can help us over the pitfalls.  They are not perfect.

Are they usually family or strangers who decide to help us? How many do we usually have?

Spirit guides are NEVER our family.  When spirit was on the earth plane, how well did you listen to their advice?  Why would it be any different once they have passed?  So to find someone with whom you could partner and listen for advice, it could be a challenge among family members.

Spirit guides come on a vibration/energy of compatibility.  They are someone who recognizes your struggles and perhaps had similar issues in their lives and have figured out how to overcome the challenges.  In that way your spirituality can be enhanced and encouraged by this contact.

So how many spirit guides do we normally have? HOw are they suppose to guide us if most of us can not communicate with them to recieve their advice in the first place?