Hi Anita, I'm not a teacher, so I'll answer as a native in Hebrew -
the dot will be under the letter that comes before the yud - not under the yud itself. the yud is like a vowel - it will tell you how to pronounce the letter before (ee) -
מי, לי those are mee and lee and the dot, if you have it comes under the m and l.
But yud can also be by itself and then it will have it's own dot or other sign under and will be pronounced according so for example in the word handle: ידית you will have a dot under the ד which will read as dee, but a קמץ under the first yud which will read like ya.
Hope it's clear