Lots of good responses already, and to re-iterate and add my $0.02:

* Before raising funds you have to be able to easily communicate your idea, and in most cases, show some kind of traction - this can be some wireframes, click through-prototype, or even scanned napkins of that the screens look like

* At this point I'd recommend getting the idea out of your head, and into something that's an input for the next stages of development. If you're comfortable with creating wireframes, you might want to check out https://www.sketchapp.com/ in order to create all the screens that make up your idea. I've worked with founders for this stage, and it's critical to be able to export what's in your brain into something shareable/tangible

* Validate, validate, validate - once you have screens, share them. Once you have a click through prototype (i.e. Invision), share that, etc.

* Having all the screens is going to be imperative to being able to design the supporting architecture and make technology choices. i.e. is this a standalone app, or does it require a backend (DB in some server, cloud). Should this be iOS only, Android only, all of the above?

So, my prescriptive statement: export the idea from your brain into something shareable if you haven't already, get someone technical to help ask the hard questions and help with technical strategy. Get lots of validation. If it makes sense, build MVP in the most economical way possible (even this has a lot of "it depends" though).