I sort of agree with Su.Ki., It's an informal idiom that gives the idea that something is not whole or complete, of maybe you are not too sure about it. Similar to "somewhat",
Ex. The movie was sort of boring (it wasn´t all dull, but it wasn´t awesome either)
I sort of thought so too. (I agree, but not strongly)
-Do you like it? -Sort of (yes I like it but not a lot, not a strong opinion)