Out of all sentence ending particles, I cannot really pinpoint what や means. I don't meet it often (or maybe I don't have enough experience or exposure) and in situations which don't really explain themselves. Also, is it a real particle anyway?
Some examples I recently found (from books):
「くつろいでくれや」
「それが実はアイロンではないからや」
I hope those examples make sense without the context. I know that those kind of particles are hard to explain but any explanation is welcome.
We are actually discussing TWO different kinds of 「や」 here, which is probably why you seem more confused than you should be.
In 「くつろいでくれや」, the 「や」 is a colloquial (and almost exclusively masculine) sentence-ending particle for 1) imperative, 2) invitation and 3) request. You are saying "(Please) make yourself at home."
Note that it attaches directly to the imperative form of a verb (「くれ」 in this case).
In 「それが実{じつ}はアイロンではないからや」, the 「や」 is a dialectal (and gender-neutral) sentence-ender mostly for Kansai. It expresses affirmation and it is the equivalent of 「だ」 in Standard Japanese. "That is because it really is not an iron."
