How we can develop a simple android app to showcase of our products.

The web has many many tutorials that cover writing simple Android apps, so it's unrealistic to expect anyone here to write another one.
Google for tutorials, pick one you like, and try it.
If you get stuck then come back here, show what you have done so far, and explain what's blocking you. Someone will help.

I think before you write such an app, you should complete your web site which is your showcase. This way you get coverage on PCs, Chromebooks, Android, iOS, Apples and even smart TVs.

You won't get that from an app.

Just create a website the same way everyone else does!

Why would anyone download an app when a website can show them all they need to know???