Help coding an Android E-commerce app

I would like to start my own website design/development angency, incorporating app development also. As i live on a small island in a small territory there is little to no competition in that field…
My passion is learning to build great android applications.
What I would like to kno is how I go about building a companion app for an existing website
Can all the coding be done in java or would I need to implement another language (JS for example for internet interactions)
Any tips, pointers or general advice on where to start would be great. In detail guides or tutorials would be even better :blush::blush:

From job interviews I noticed React Native gets used a lot for App development, which is based on the Javascript language. So, I’m not sure about Java

On Udemy I found a tutorial that goes into detail on App development for both Android and IOS:
Tutorial isn’t free, but would recommend it, Javascript knowlegde is also recommended :stuck_out_tongue:

On Youtube there are some React Native tutorials scattered around as well. Hope this helps!