Rhythm is what makes each song different from each other. There would not be music without rhythm.
Rhythm is created when you play some notes long and some notes short.

To learn good rhythm, you need to know how long to hold a note down before you let it go.

When you play the next song, you will hold each note down
long enough for you to say "tick-tock".
When you say "tick-tock" you are giving each note one beat.

Make your voice sound like the rhythm of a clock. Slow and steady, never speed up, never slow down, never stop, and never pause.

Make sure your finger plays the note at the same time that you say "tick" and don't let go until you are finished saying "tock".