They have the same meaning but "for instance" is mostly used if you want to give specific example that talks about events while "for example" is mostly used for objects or things.

There is a little difference between the two. As an example, look at the following sentence: I know all taxis are yellow in Rio de Janeiro. I can say, for exemple, that taxi you took yesterday in Rio de Janeiro was yellow. Now in São Pulo, for instance, I cannot do the same because not all taxis have he same color.

They're basically synonyms used in phrases in order to avoid repetition. But, I do believe that "for example" is slightly formal, while "for instance" is both formal and informal.