Is it true that we get pimple, if we have dandruff in our head?

Sometimes they go together, but not always.
Both are usually from clogged pores and clogged oils, and need to be kept clean with unscented soaps, rinsed very well so there is no residue, given healthy exposure to clean fresh air each day, and a good healthy diet. Maybe some vitamins too.

It's true they go together but it's all about how yo treat your skin. Get a face washer and dip or in boiling water the ring it out and lay in on your face, when it gets cold dip it in the boiling water again. Repeat this 4 times, don't eat too much junk food this will cause pimples. Don't pop the pimples as this will cause infection/irritation, and lastly get plent of fresh air but wash your face after being outside otherwise the dirt can get into your pores and cause more pimples.

In other words no you do not.