First, you gotta get it in your head that running isn't just about the legs, it's also vastly about breathing. If you don't inhale enough air at the right time not only will your legs hurt you'll also feel a sharp stab in your lungs. In fact, that's how people who're just starting this jogging life often stop running; it's not that their legs are giving out, it's just they're suddenly having problems breathing and they can't keep going.
So practice proper breathing. Inhaling and exhaling deeply into your lungs at a constant rythm. That's step number 1.
Step number two is to plan your route and stick to it. Choose a 1 mile route, from point A to B and dominate that first. Start small, then increase every two days of running. 'Til you get to 3 miles. If you feel it's taking too long then consider adding half a mile per running time. The key to this step is remembering that legs can take a lot of beating before they shut down.
Running is a really huge mind effort, because you gotta drown out the voice that keeps telling you "yo this is good, you've already done more than enough, okay stop breh!". The people that stop running because their legs actively stopped working is super rare, usually the defeat is always in the mind first before it's in the body.
Step three is to always remember to alternate between jogging and running. Running requires you to breath a whole lot more quickly, jogging is so you can regulate that breathing. So if your breathing is regular don't be afraid to speed up, if you're feeling discomfort breathing then slow down from running to jogging.
This goes back to step one which amounts to avoiding that sharp pain in your lungs which is a reminder that your body is lacking in oxygen.
Reaching a specific distance isn't about time at first, it's about conditioning your body. Once you can run these 3 miles you wanna run comfortably, then you can start working on lessening the time it takes you to do so.