Thanks Rarst and Stackexchange, one image tell us how to correctly use
query_posts()is overly simplistic and problematic way to to modify main query of page by replacing it with new instance of the query. It is inefficient (re-runs SQL queries) and will outright fail in some circumstances (especially often when dealing with pagination). Any modern WP code should use more reliable methods, like making use of
pre_get_postshook, for this purpose. TL;DR don’t use query_posts() ever;
get_posts()is very similar in usage and accepts same arguments (with some nuances, like different defaults), but returns array of posts, doesn’t modify global variables and is safe to use anywhere;
WP_Queryclass powers both behind the scenes, but you can also create and work with own object of it. Bit more complex, less restrictions, also safe to use anywhere.