Waterloo East is next door to London Waterloo (there is a covered footbridge between the two). I think they were built by competing historical railway companies, but don't have time to look for the details right now. The main Waterloo station also gets trains from the South West; London Bridge gets trains from the whole South coast (e.g. Brighton and Southampton), as well as Kent. I use London Bridge for work, Victoria for shopping and change onto the Waterloo line at Clapham Junction for visiting my Mum.