???? chotto is an adverb along the lines of "a bit ~", as in "This steak is a bit tough."
?? ma-tsu is the verb "to wait."
??? ma-tte is the like a mild command, along the lines of you telling someone to wait.
Putting them together gives you, as PingPongPang stated, something along the lines of "(wait) just a second" or "hold on." Tone of voice determines its force, just as in English.