Tiny confusions

Hi everyone, I'm new here and and it's nice to meet you all...my name is Eric and I'm a Nigerian....I hope we get to know each other more as time goes on. Now over to my post Why is it said to be " give him his book and not give her she book"? Why are stuffs carried by ships called CARGO and those carried by cars called SHIPMENT"? Why can I shot a dear in my pajamas when pajamas is not actually a place? These are some of my tiny confusions..... English can be really wierd