How to read Mongodb entries in plaintext?
You are seeing "plain text" documents right now, in json format. Command db.coll.find() shows all documents (in batch of 20 documents). If you want those word wrapped (easier to read) add .pretty() to end of line 

db.coll.find().pretty()


of course all these documents are in bson (binary) format in database and if you want to see that, use mongoexport.

When you insert document, if you don't specify _id, it is added automatically. Rest of document is just like you inserted it.