There are two main differences that I know of: 1) "To marry" is transitive-- it requires a direct object. Example: "Camilo is going to marry Sarah." (In modern, idiomatic English you cannot say "Camilo is going to marry.") "To get married" is instransitive. Examples: "Camilo is getting married." (You can still include information about his fiancée in a prepositional phrase beginning with "to": "Camilo is getting married to Sarah.") 2) While "to marry" most commonly means "to become a husband or wife," it can also mean "to preside over a wedding." That is, the rabbi, priest, ordained minister, or legal official can also be said to "marry" the couple that is getting married. ("To get married" does not have this ambiguity.)

I don't know!

Just to add what Dave has said: I presume you don't have any problem with the two transitive uses of marry: 1) William married Kate or 'Will you marry me?' or 2) Father Brown married the happy couple in the village church. and that you are asking about the difference between: 'They married in London in 2008' and 'They got married in London in 2008' ? The difference is one of style and formality. The first is old-fashioned and literary-sounding, and is rarely used nowadays, except in formal situations, legal language etc. The second is usual in everyday informal and neutral contexts. So while 'Let's marry' and 'John and Emma are marrying' are technically correct, a native speaker wouldn't use these constructions - you would say 'Let's get married' or 'John and Emma are getting married' instead. I hope that's clear.