BEGIN or START
Both words mean the same: to start doing something. Begin is more formal than start.
‘She started / began learning classical music when she was 5.’
‘I don’t think we should wait for the other guests. Let’s begin.’
There are some cases where you use ‘start’ and not ‘begin’.
We start a journey and not begin.
‘He started on his journey early one Monday morning.’
Start working and not begin working
‘The scooter didn’t start.’
The word ‘commence’ carries the same meaning as start or begin, and like begin is formal and used only in certain cases.