I have an original app idea that I’d like to draft up on paper, what tool or template can I use? Also, how can I protect my idea when sending it off to a designer/developer?

Instead of random illustrations, is there a tool or template (like a popular scope document or brief) I can use to guide me? I'll then be sending off the doc to a developer to create, in which case I'd like to protect my idea, how would I achieve this? I can finance it and I have time to work on it. Just looking on how to get started. Cheers in advance.