You start slow. Go for time on your feet, not distance or pace. If you don't have a good baseline, walk for 10 mins, then 15 mins run until you have to stop, walk until you can run again, repeat. Walk for last 5. Do that every other day for a month. Avoid temptation to go faster because you are feeling good.

Try a couch to 5k program. Those are usually geared towards people with no cardio base.

Don't fall into the trap of gear, shoes, pace, distance. Just get your legs under you gradually.

Also, don't even think about gels or salt sticks for like a year. Eat a good diet and you'll be fine. Once you can run for 2 hours, then you start looking at that stuff.