Html

Question

Is HTML essential for an app developer or it's not useful..... I finished the HTML course and presently studying CSS

Answer 1

What kind of app? A web app? A movie app? Windows app?

Answer 2

HTML is a markup language used to develop Websites.
HTML itself can be used to develop a web app but it will look like a child drawing on a sheet, to make it look good, you may need CSS.
Secondly, You need JavaScript which adds logic to your website, though JavaScript is not necessary to build a web app but still it's one of the most important languages used in web development.
In terms of developing a mobile app, you may use Java/Kotlin.
For IOS app, Swift.
For windows app, C# or more.