Do I have to code HTML?

No, you don’t have to code any HTML or JavaScript code to get HTML pages out of Plex-XML.

As long as your pages are using a default design like insert, update, delete, find/browse (grid) you are able to get HTML pages without any extra work. For some pages you have to add some XSLT snippets to get customizations like extra buttons, click events, tab-dialogs or master details. But most of this customizations are predefined snippets to hide the complexity behind it and they are easy to use without deep knowledge of XSLT.

Only if you need to build pages with special logic (e.g. drag&drop) or a special design you have to use HTML, JavaScript and /or XSLT. And you are able to do it without any restrictions.

Most customizations you need on the default pages like field order, labels or search operators are done while using the formats.

See below a screen shot of the default layout you get without any customizations: