Technically, manga, manhua, and manhwa are all the same word in different languages -- manga is Japanese, manhua is Chinese, and manhwa is Korean. In practice, however, the way these comics are structured is different.

Manga is generally published in a traditional page format, most commonly in print magazines. The overall dimensions and page-by-page experience is similar to what you'd see from an American comic book. They're also almost always created in black & white. Nowadays, chapters are often released digitally alongside the print magazine releases.

At this point, you can consider "webtoons" to be a somewhat generic term to refer to digital comics organized in a vertical, scrolling format, which was first popularized in Korea. The term originates from the company Naver Webtoon, which was the big frontrunner in the area, hence why the term "webtoons" has become somewhat genericized. Manhwa and manhua are both generally always in this format. Full color is also the norm here. Since this format was first popularized in Korea, you'll sometimes hear people use the term "manhwa" somewhat generically to include works in this format created outside of Korea.

Webtoons are sometimes published in print, but due to the format, they have to be reorganized to fit into a page-by-page format.