Translation:There are all types of people there.
The word there has different meanings in English. One is as a placeholder much like det where you could feasibly replace the word "there" with it or that... eg "there/it/that is/exists a cat on the windowsill". The other is as a position/direction. eg "Over there is/exists a cat on the windowsill."
The word där means "there" in the latter sense of the word. So this sentence doesn't just say: "There are all types of people" but rather "There (as in "in that place"), there are all types of people". We then move the positional "there" to the end of the sentence to make it read clearer in English. Or we could instead say: "There, (comma to clarify we mean "in that place"), exists many types of people," though this is slightly more ambiguous.
(PS I put the word exists into the sentences not because that is in any way idiomatic English but because it helps remind me the meaning of finns... I don't know if other people do this but it seems clearer to me to translate it this way in order to separate it from är/står/ligger etc...)
This is just a guess, but perhaps 'det finns' is more of a figurative/general 'there is', and 'där finns' a more literal/specific one. So 'det finns' might be like, 'There are many different plants [in the world]', but 'där finns' would be 'There are many different plants [there in my garden]'. Someone please correct me if this is wrong; I'm curious about the answer, as well.
Can the subject be omitted in this case? Där is like a local adverb and all types of people is the object. May I omit the det? German has a similar verb (es gibt) and sentence structure ,but in a case like this they would require the subject to be written in the third position iirc.