Exactly what happen when they occur?
Mining stopped?
Coin balance of owners will be transferred to new wallet automatically?
People posted plenty of technical links above me. Here is my ELI5 version:
1. Hard fork - when number of people decide to ignore longest chain an mine on a certain block ignoring everyone else on the network for some reason. One bright example of hard fork is BCash - it is a hard fork of BTC supported by number of people.
2. Soft fork is when everyone agrees to roll back or change rules starting from certain block height and changes become effective from block N, but the actual fork does not happens.