How do I file an exemption for my LLC prior to becoming an S-Corp?

I know what LLC means, but please explain what S-corp is.

Also, it would help to have a little more information about what type of businesses this concerns.

I am not a tax expert. But, by my posting a response to your question, it is more likely to get noticed now because it will be more towards the top of the list of questions that need to be answered.