By saying "i want to create an app for promoting and growing my business" and the context in general, my understanding is that you want someone to create a website for your business.
Most likely you will need ongoing support for changes and maintenance. And a hosting site.
Is that correct?
The starting point is for you to write up a list of requirements. In other words list out as much information as you can regarding how the webpage should look, what options/menus will be available to visitors. Will they be able to join in some manner to look at what you are selling and place orders?
Go online and look for websites that are similar to what you would like your website to be. Gather ideas accordingly.
Then submit your requirements to website developers in your area and request information regarding their recommendations and potential costs. And how long it all will take to code, test, and post.
Also ask about other websites that they have developed and may be continuing to support.
Request the names of other customers so you can contact those customers but be skeptical about what those customers tell you....
And, just having a website (no matter how good) does not mean that customers will come running to buy your products.
However, a website that is not well designed and poor in appearance will certainly drive people away.