I.  Behind a noun:

• noun1 + や + noun2 (+ や +  noun3 + や )+ particle + predicate  = noun1, noun2, (noun3) and others.
田中や加藤と話した。I talked with Tanaka, Kato and others.
醤油や塩はあります。I already have soy sauce and salt.
 
※The list of nouns can be indefinitely long.
 

• verb-plain + や + (いなや) = just as soon as something is/was done
家に帰るやいなや、シャワーをあびた。
    I took a shower as soon as I got back home.

※や does not occur with any other particle.

※や as a conjunctive does not connect sentences.  In order to link two sentences, そして、それから、. . . し are used.
        お店へ行きました、そして果物を買いました。I went to a store and bought some fruit.

• とlists everything, but や implies other things also.   Go to to (と)
りんごとバナナがあります。There are applies and bananas.
りんごやバナナがあります。There are applies, bananas, and others.