*take my words for it*, what does it mean?

you ask a lot of good question :)
ok,
"take my words for it" = asking something to agree with you, or accept your suggestion or approve your idea ...
examples :
"Mother, I know sister broke the glass earlier, please take my words for it."
"Boss, I have years of experience with this subject, and I said the stock market is going to crash. Remember to take my words for it."
:)

*take my words for it* = [我保證]咁上下 la. 美式英語. 等同 I swear. 不過唔係人人都對任何一個人發誓 ka ma. 故用 *take my words for it* 比較好 lor.

example = I am ensure that the product that you need will be here on or before saturday. Take my words for it!