There is just no good English translation for כלי -- you can try utensil, apparatus, implement, tool, gizzy, thing-a-ma-bob... they are all correct in the right context, somewhat misleading in the wrong context. The gemara even uses it to mean "clothing." So let's just leave it alone. When it comes to the requirement for טבילה, the rules seem straightforward enough: The Torah requires that when a Jew acquires a metal כלי from a non-Jew -- that is, ownership is transferred from the non-Jew to the Jew -- then the Jew needs to immerse that כלי in a kosher mikveh before he uses it. Chazal added glass כלים and some stringencies about the mikveh. Simple enough. There are two details that make things a bit more interesting. One, "use" means "for its intended purpose", but has nothing to do with contact. For example, If it starts hailing as you are walking to your car with your newly purchased (from a non-Jew) griddle pan to your car, you are certainly allowed...
This is a paraphrase of the pasuk in t'hillim 84:7 -- "mei'chayil el chayil" -- which means "from strength to strength". In this case, it is my thoughts and ideas to those who are strong enough to be interested :)