I used to cycle a lot in my early teens, mostly to school and back,,a fair few miles. Now im in my early 60s i still think im pretty trim and fit but in need of some aerobic improvements i dragged my mountain bike out of the shed.
Lessons i learned
Dont spend a fortune on a bike at first. Get your old hack out of the garage. The early stages of taking up cycling involve pain and discomfort. Its as simple as that. Whether you do that on your old hack or a 2 grand new bike is immaterial. You have to sweat through that early stage to get to a certain level of fitness where you can enjoy the ride and you can do it without the pain.
Learn basic cycle safety skills. Im in favour of his vis,a lot arent,,your choice.
Make sure your bike is well adjusted. Seat height is critical,also make sure tyre pressures are well up.
In the early stages ride a set route and use a phone app to measure performance. This should show continual improvement which will encourage you and demonstrate clear results
Remember,its never a crime to change down so if your feeling the pressure on a slope, drop a gear..
Most of all keep going..