Hi Arif,
> What could be the best learning path to become more proficient in Web Apps and Mobile Apps?
I don't think there is a single "best" learning path, as people are different and have different skill sets to begin with. Also, it depends on what you want to learn exactly. Do you want to learn more about web and mobile apps in general? Are you interested in development work for these types of apps? Did you have a specific business workflow you want to support with the apps?
I suggest starting here to learn about the ArcGIS Apps, Apps for Everyone so you can get an overview of the various ArcGIS apps available.
To learn more about the "web apps", this video might be a good place to start,
Building Great Information Products with ArcGIS Online - YouTube
To learn more about the "mobile apps", start with this video,
ArcGIS Apps for the Field: An Introduction - YouTube
There are also many great training resources available online at the Esri Training site, https://www.esri.com/training/ and Learn ArcGIS.
Hope this helps,