1This (a thing, person, or idea near the speaker) — a pre-nominal demonstrative used before a noun.
この本はとても面白い。
This book is very interesting.
この人は私の同僚です。
This person is my colleague.
この問題は少し難しいですね。
This problem is a bit difficult, isn't it?
このアイデアなら成功すると思う。
I think this idea will succeed.
2This (as in "this past" or "these"), referring to a recent period or the immediately preceding stretch of time.
この数年で生活が大きく変わった。
Life has changed greatly these past few years.
この夏は例年より暑かった。
This past summer was hotter than usual.
3An emphatic, insulting use meaning "you ..." (e.g., このやろう), used to accuse or insult someone.
このやろう、ふざけるな！
You bastard, cut it out!
この嘘つきが！全部話せ！
You liar! Tell me everything!