From iTunes, how do you select the songs you want to put on your iPod?

I'm not computer illiterate just so you know, I know by clicking on the little box on the left of the song you can select to add it to your iPod. BUT it doesn't do what its suppose to do. It doesn't allow me to add those songs. It just picks a bundle of random songs and adds those. How can I change the settings to JUST add the songs I have selected to my iPod?