A vav-conversive (also called a “vav-consecutive”) is a conjunction and is usually translated “and”. It is easily distinguished from a simple vav conjunction since it always has a vav with a patah under it and a dagesh in the following letter. more
וְשָׁמָֽיִם a simple vav conjunction
וַיִּיצֶר a vav-conversive
The key point to remember is that a vav-conversive converts a YQTL from a future tense to past tense (these forms are often called a “preterite”). The following rules are helpful for identification: