Hi Kinson!
When it comes to these synonyms, the differences can be a little subtle, but I'll try to explain them.
Geek-someone who is socially awkward, and often does not fit in with mainstream society because of this awkwardness
Nerd-can be similar to a geek, though less negative and may not actually be socially awkward (it depends); nerds are distinguished by being extremely interested in certain hobbies or interests, such as computers, games, etc.
Dork-more negative than "geek" or "nerd"
Dull-different altogether; someone who is "dull" is simply boring or uninteresting
I would put "dork", "geek", and "nerd" on a spectrum, with "dork" being the most negative, "nerd" being the most positive," and "geek" being somewhere in the middle.
Like I said, the differences can be subtle, but I hope this helped some!
Best,
Jacob