Although your specific question would likely result in [recommendations for sites and resources](https://webmasters.stackexchange.com/help/on-topic), which is considered off-topic on the main site (but not in our [chat room](https://chat.stackexchange.com/?tab=site&host=webmasters.stackexchange.com)), I do think there are _strategies and techniques_ that could be conveyed to help demonstrate website designs & layouts, modifications & improvements, performance & tracking, ads & marketing, beta testing, etc... to others, which would seem to fall under the [responsibilities](https://en.wikipedia.org/wiki/Webmaster) of a webmaster. 

Although there already exists tags for [development](https://webmasters.stackexchange.com/questions/tagged/development) and [web-development](https://webmasters.stackexchange.com/questions/tagged/web-development), these would seem to be more concerned with the _development process_ than conducting _demonstrations_.

I therefore created a [demonstration](https://webmasters.stackexchange.com/questions/tagged/demonstration) tag and added it to your question, which will remain since it has an upvoted answer there. For its description, I added:

> Anything related to the demonstration of a website, including: website
> designs & layouts, modifications & improvements, performance & tracking,
> ads & marketing, beta testing, etc...

I've also created a [demo](https://webmasters.stackexchange.com/questions/tagged/demo) tag and added it as a synonym to the `demonstration` tag, so that if a user types `demo` they'll be provided with the `demonstration` tag. The reason I didn't chose`demo` as the main tag is because it's often used in reference to _software demos_, as the [demo](https://stackoverflow.com/questions/tagged/demo) tag on Stack Overflow indicates.