It's easy although you may get impatient. It's similar to riding the bus in any city.
Just go to the platform or dock, wait in line, and board the bus or boat or monorail.
No fares are collected on board.
Do be aware that going from one resort to another resort requires a transfer. Going from a park to Downtown Disney requires a transfer (at a resort). Disney has suggested allowing an hour and a half for these trips.