I want to clone this repository and used the command:
git clone https://github.com/wildfly/quickstart/tree/master/helloworld-html5
It doesn't work. I guess the URL isn't the format that's right. How can git clone this repo? Thanks.
Looks like you're looking too deep into the repo.
Try this:
git clone https://github.com/wildfly/quickstart.git
It should have all the files you need.