I navigate to the definition of a function by right click on the function name then select "Jump to Definition". But I don't see a way to get back to where I was ... is there a way?
Not in the current version of Xcode. There was a huge discussion about this on Apple's Xcode mailing list last week. Look for the thread "how do you go back".
If the definition is in the same file, I don't think there is a way to get back. But if it takes you to another file you should be able to use the < back button above the editor.