Using a keyboard pedal makes your playing sound smoother. It is recommended that you start using the pedal only when you you have mastered the basics of playing songs eg with melody and chords, so that you don;t try to learn too much at once.
More information is in the lesson 'Using The Pedal' in the PERFORMANCE / PLAYING TIPS section 7b of the Bundle.
You can purchase a branded pedal eg Yamaha or a low price pedal such as:- https://www.gear4music.com/Keyboards-and-Pianos/Alesis-ASP-2-Sustain-Pedal/2F57