What's an Instagram?

So I have joined Instagram, inspired in part by Kei, and in part by desire to get in on Japanese toy poodle Instagram. If I have my way, Bisou will soon be a huge Japanese celebrity. This is unlikely, because a) brushing her every other day and getting her groomed every month and a half doesn't add up to her looking like the glamorous Japanese poodles Into The Gloss profiled, and b) she doesn't have the wardrobe. There were absolutely stores in Tokyo that sold amazing small-dog outfits (including kimonos), but Bisou wasn't there with us, so we didn't know her size, plus I don't think these outfits would fit with her lifestyle, which principally involves trying to eat deer poop when I'm not looking and chasing squirrels up trees. (Not, thankfully, in that order.) Of course, I'm sure the poodles of Nara present similar challenges...

But I can't figure out anything about Instagram. How does one search it for people, images, anything? Also: What is Instagram etiquette? People are adding me and, on the wild off-chance that I ever figure out the mechanics of adding people back, whom is one 'friends' with on this site? Part of what inspired me to join was that I felt like it was a way to avoid spamming Facebook with every last photo of my amateur Cooking With Dog existence. I can't imagine most of these people would want to see any of this. I don't flatter myself that anyone's losing sleep over whether I follow them on Instagram or whether I restrict my follows almost exclusively to people who pose large groups of lap dogs in fields in Japan. For all I know, these are automatic adds that happen when someone one is Facebook-friends with joins the site. But the situation I don't want to get into is feeling like I'm spamming people on Instagram by posting... the very sort of items I got on the site in order to post.