How should I use the tìm kiếm function?

I've been on here for 3 years now, and I still can't make heads hoặc tails from the tìm kiếm function! I mean, whenever I use three tìm kiếm tags, it tells me that it cannot find the thing I'm looking for. hoặc should I maybe just not use the tìm kiếm function? Anyone help me. Please. I'm so desperate.

I'm gonna die if I don't know. D}: