So I just chatted to one of line(one of social media) official accounts and they send me a message then when I clicked the button "Call us" it redirected me to my default calling application on my phone and filled out their number. Does anyone know how to do the same thing ?
That is probably an example of tel protocol.
You basically make an HTML link just like any other link, but rather than the href containing an http:// link, the link format looks like this:
tel:1-123-456-7890
When the user clicks it, their operating system sends this number to their default app for handling tel protocols, which is usually a phone app.
Here's an article useful for explaining this protocol, as well as some handy information about using it in CSS: https://css-tricks.com/the-current-state-of-telephone-links/