It merely ensures that your code is without HTML or CSS errors.
If you are wondering what the difference is, an analogy from normal human language will hopefully make it clear.
I always validate the template for my pages when I make a major design change.
I try to validate my pages each time I make modifications, although I must admit that I sometimes forget to do so (with the occasional disastrous consequence; Murphy's Law doesn't spare webmasters).
Semantically, however, the sentence describes a different thing from what you meant.
HTML and CSS validators are designed to catch the first type of error, exemplified by the grammatical error of my first sentence.
Simply point your RSS feed reader or a browser that supports RSS feeds at https://by Christopher Heng, Whether you design your web page using a visual web editor like Dreamweaver or Blue Griffon, or you code HTML directly with a simple text editor, the generally recommended practice is to validate it after you finish designing it.