Suffixes are one or more letters, words which are added at the end of a word to modify the word's meaning. -Or and -er are examples of suffixes which when added to another word can change or modify the meaning of the word completely. For example, when you add -or to words like advise, protect, direct, it becomes advisor, protector and director. Also when you add -er to words like play, it becomes player. This shows it has changed the meaning of the word 'play' which is a verb to 'player' which is a noun.
Another difference is that, both -or and -er are used to differentiate between American English and British English. There are so many words in America English which are not acceptable in British English. For example, advise is a verb, but advisor can only be acceptable in America English if it is written as adviser, while adviser can only be acceptable in British English if it is written as advisor.