1. Figure out which ideas you consider as best among "so many" and nail down on those.
2. Do a competitive analysis on if any similar apps are already there in the market or not. If there are some then thing if there is a space for another similar offering, and if yes then what you can offer differently than others.
In case there is nothing similar existing already, you've the advantage of being initiator but you need to be wise to position it better.
3. Decide your first target group of users, and geography. I understand you may think your app can be used worldwide and rightly so, but start focusing on a certain area and achieve traction and then go big.
4. Now, document your app idea in the most simplest ways possible, you can following this article to know how to write app specs - http://www.agicent.com/how-to-write-app-specs.
5. Put your specs to potential good app development companies (I don't suggest going with freelancer way if you've not worked with them in the past, also app development need a team and not a single guy so go for a company) that you can search in forums like these, or via google. Get a cost estimation, or use and handy tool like this to quickly estimate app development costs - http://www.agicent.com/app-development-cost-calculator
6. Compares the quotes, experience, quality, and overall offerings of the developers. Select the ones good on all parameters, and whom you can use for long term (another reason I suggest going with an app development company).
7. Hire the developer, and ask for a trial work first (we offer free trials always).
8. Start the development, see your app's progress every week until it goes to the store. create a good landing page also, do some good on page optimization of both app store page and landing page, try to get some press coverage and learn on this path.
Every suggest I've given here is a topic in itself and lot can be discussed on that, so I suggest you to start small, learn, partner with right people, and grow as you learn.
Following is a good post for first time App entrepreneurs like yourself https://www.linkedin.com/pulse/hiring-app-development-companies-read-first-sudeep-bhatnagar.
I own an app development company and we develop apps out of just idea for entrepreneurs like you only, so feel free to get in touch with me for any further discussion.