My AirPods will not connect what so ever

Okay so one night my friend gave me her old AirPods but they were new and everything. So I tried to connect them to my phone but after it said it was connected they immediately disconnected. So I tried again then it told me to forget the device, so I did. Then I tried to connect it again and it did the same thing. So I did some research and I rested my phone and the AirPods and tried it again. It still didn’t work. So I don’t know what to do because it will not even connect to my friend’s own device.