I've been watching videos on poker online recently and they all talk about certain hands being at the top of ones range and bottom and about opponents making polarized bets.....I don't really understand this so I was wondering what they mean by these things??? Giving an example would be much appreciated.....I have been reading some poker books recently and none seem to cover these topics so that's why I am really curious? Also, do these concepts apply to all stakes or just the high stakes where people actually know what their doing? Thanks.

range = set of all possible holdings a player can have in a given scenario. For example, when tight player raises utg, he's gonna have a range of somethig like 88+, AJs+, AQo+, KQs.

Being at the top of your range = having one of the strongest holdings from one's range, in a given example top of utg's range would be QQ+, AK (or however you want to define "top)

Polarized bets = betting only with top and bottom of your range in a given scenario, ie, strong hads and pure bluffs. This doesn't really apply to preflop, but postflop in general all of your bets should be kinda polarized, for example when you decide to continuation bet flop, you should do it with top pair or better and hands that missed, while checking hands like middle pair.

Suppose you're on the river and the board is QJ477 and you bet flop and turn. On the river, your best hands would be QQ/JJ that flopped sets and rivered a boat. You'd bet these (the top of your range), because you want to get called by worse hands (like AQ/KQ). It would be a value bet. At the other end of your range would be hands like KT/T9 that had OESDs that didn't get there. If you bet these, it would be a bluff, and you want to make villain fold better hands (like AJ/KJ). With hands in the middle of your range, you'd often check, because the hand can win at showdown, but is unlikely to get called by worse if you bet.
Hence, you bet "polarised", with value bets at the top of your range, bluffs at the bottom, and you check back the middle.

awesome feedback!!! thanks so much!