The main use of the exclamation mark is to end sentences that express:
 An exclamation:
‘With a fixed bayonet! A fixed bayonet!’ he repeated incredulously.
 Direct speech spoken loudly or shouted:
‘The first one … the first!’ everybody yelled.
 Something that the writer or speaker finds amusing:
Her son was the biggest poacher – he was a devil: he’d rob your house in the middle of the day and let you see him!
It can also be used in brackets after a statement that the writer finds amusing or ironic:
I look ruddy, muscly, well covered (!), and just, shall we say, solid.
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