Like ね (ne), you can add よ (yo) to the end of a statement, but よ makes your statement sound assuring. It gives your statement a sense of authority. You can think of よ roughly meaning "I tell you" or something along those lines.
わたしのせんもんはにほんごですよ。 (watashi no senmon wa nihongo desu yo)
My major is Japanese (I tell you).
ほんださんのねこはちいさいですよ。 (Honda-san no neko wa chiisai desu yo)
(I assure you) Honda-san's cat is small.
That's all there is to ~よ. かんたんですよ。(It's easy, I tell you!)