Are you sure you have access to internet ?
More seriously, uploading a video on a app is heavy. A good internet connection is a must. The best would be to be with Wifi but 4G works also of course. The faster your network is, the faster your video will upload. It also depends on the length of your video : the longer, the more the upload will take.
If it takes really too much time (like one hour or more), don’t hesitate to quit and restart the app (warning : don’t log out or you will lose your upload).