Sometimes you can get a puncture. But don't worry it's easy to fix!
You can purchase a new inner tube here - https://www.edwardsandcobaby.com/spare-parts/oscar-wheel-parts/tyre-inner-tube/
To change the inner tube yourself, watch this video - https://youtu.be/fvLCsqYIqgY
Most bike shops will conduct an inner tube replacement for you. There may be a small charge for this.
REMEMBER - always use your tyre pump to inflate the tyres. NEVER use a tyre pump at the petrol station!