Junk mail is a term used to describe letters or advertising products which are sent to people who have not asked to receive them. It can also apply to email.
Examples:
Why does no one send me real letter
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To crack on is to continue doing something as quickly as possible. The phrase is also said to encourage someone to do something or start doing something.
"Say cheese!" is an expression used by photographers to make people look like they are smiling - because that's the shape the mouth takes when you say the 'ee' sound in the word 'cheese'.