There’s nothing wrong with the bike or the gearing. A 39-24 gear is easy enough for you to get going.
You need to build an aerobic base, the rides that are slow (and eventually long). This is the foundation that everything else is built on.
As some have suggested, forget the technical/statistical side of it and just ride, gradually increasing the time and distance. The more you ride the better it will feel. This foundation will also take time. It takes many days/weeks/month and years to build a really good base.
Most of all, have fun. Stop riding while you still enjoy it. That way you will want to come back for more.