가레 is not a word as far as I'm aware of, except as a way of writing a foreign name.
가레산스이 is a Japanese rock garden.
고래 is a whale.
구려 is a grammar point that seems a little advanced. It means "I advise that you...", "You had better...", and "You may...". It is also used to make an exclamation. It also seems to be slang for "(this) sucks/is awful/is lame/blows/wack!"
고구려 is a time period in Korean history.
그려 is a conjugated form of 그리다 (to draw, to paint a picture). So it's exact meaning would depend on how it's being used in a sentence, but it will basically be "draw/paint". Of course 그리다 is a part of some other expressions, so it could have other meanings too. But this is the most common. 그려 also appears to be a more advanced grammar point/vocabulary term as well.
For the advanced grammar, I wouldn't worry about studying it or learning how to use it at this point.
As for the other words, you would use them when appropriate^^
For example, if you're talking about a whale, you would use 고래.
If you were talking about a Japanese rock garden, you would use 가레산스이.
They be similar in spelling, but they are certainly not similar in meaning.
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