Let's assume you are talking about getting funded to create a full version of the app. Contrary to what others are saying, you are likely going to need a prototype in order to clearly demonstrate what you are trying to accomplish with this app. VCs and investors like to see a minimal viable product before any discussion about funding can begin. Now, what prototype means is a very wide range of things. It could be a simple as a sketched mockups of each screen of your app - a paper prototype. This is actually very useful in early customer testing. You could also create an interactive prototype through a service like Invision, this will be a simulation of your app without any code written. Also, a lot depends on the complexity of the app. For instance, if you are creating an app which follows well known user experience conventions like booking or instant messaging, then it's easy to demonstrate functionality using existing apps, while if this is something completely new, then more details will need to be fleshed out in the prototype.