You got the idea. Example : I have an expertise in teaching English. (It means I'm really good at it , like an expert at it) I have experience in teaching English. (It means I've done it before but it doesn't mean I'm good at it) I hope this helps. (Btw, I don't have an expertise in English ,this is just an example :))

Yes you have the right idea. 'Expertise' comes from the word 'expert', so a person has a high level of knowledge and experience in a particular area.