How can we define the html layout as per UX? what is semantic html as per UX? [on hold]

I am new to this UX, How it defines the user experience, how to implement user experience in HTML layout? What is semantic html in terms of UX view point. Does it help to improve my site accessibility by using ux.

My need: any once can tell me how to implement the html in proper way. for example disability person need to access my webpage. in that case semantic html help for that people. so correct html element is correct place how to code or write? for this experiences(ux) required or not?