To understand secondary dominant chords on the piano, it's vital to know what dominant chords are. Generally in a song they're the first note played and the last note played, as well as comprise the most tense point. Secondary chords are dominant chords that match up with other scale degrees in a scale.
If you'd like to learn how to play secondary dominant chords with ease, check out this piano tutorial. Your instructor will start you off with the C major scale and then progress from there to make things simple.