If I start at the top of main, the variable one stores the string "two", the variable two stores the string "three", the variable three stores the string "1", and the variable number stores the integer 20.
The call sentence(one, two, 3) passes "two", "three", and 3 to the formal parameters three, one, and number. The formal parameters are different memory locations than those in scope in main. The formal parameter three stores "two", the formal parameter one stores "three", and the formal parameter number stores 3. Using those values, the println statement in the sentence method outputs "three times two = 6" (although in Practice It you don't enter in the quotation marks with the answer).
This is what Evan is saying, but I think including the quotation marks with the strings makes it clearer.