I'd be interested to know too. Guess the Globe is for global posts. The magnifying glass for when you search to which relays will direct the query to, the people would be your Following list. But really, am bit clueless too.
Discussion
It turns out that, using my earlier screenshot as an example, if you long-press on each of the icons (one at a time, from left to right, for each relay) that a notice pops up at the bottom telling us what each one is. For example, click-and-hold on the icon that looks like a bird-house and a message pops up saying "Home Feed"; the same on the envelope icon displays " Private Message Feed"; and, so on. Do that across each of the icons and you at least get their names.
As to expected behaviour when each of the feeds is switched on and off I don't get what I would necessarily expect. For example, if I delete all relays apart from one and switch off the Global Feed and Search Feed switches for the remaining relay I can end up with the Global Feed full of posts and seem to be able to search also, which is not what I would expect. Clearly, still subtleties to come to understand.