How to remember?

Since this Kanji is easy and frequently used, I recommend you to remember it as a sight word. In other words, just learn it by rote.

But if you want to know why 千＝1000, here is the explanation:

千　is actually the combination of and 十, which mean "human" and "ten" respectively. If one human can live 100 years, then 10 can live 1000. And here comes the Kanji 千.

Radical

The radical of this Kanji is 十.

Do not confuse this Kanji with:

干 which means "dry". The first stroke is horizontally left to right. But for 千, the first stroke is diagonally right to left.

チ which is the Katakana "chi" . Actually, this Katakana is derived from 千.

于 which is mainly used in Chinese and very rarely in Japanese. The first stroke is horizontally left to right and the last stroke has a hook.