voltage - Few questions about basic concepts in electronics

So I'm rather new to electronics and I'm struggling to understand some basic concepts because I picked up little information from many different sources so it's starting to get confusing :/

1. 
   

   Why does current flow from positive to negative when electrons flow negative to positive? I thought current was the flow of electron

   
   



2. 
   

   I think question 1 will answer this but why do you need to connect both sides positive and negative in order to power something? i.e. led

   
   


3. 
   

   Why does voltage keep on rising and falling in an ac circuit?

   
   


4. 
   

   I heard that ground is basically the negative side of the power source as it has 0 volatage(potential) but I thought when powered by a 1.5 volt battery the entire circuit had 1.5 voltage all around.

   
   

thank you :D