The pots are for ease of transferring the plant from the grower's facility to the pet store to your tank. If you have no plans to move the plant, take it out of the pot and plant it in the gravel. There'll be rock wool (I don't know why it's called that) packed around the roots. Take off as much of it as you can, but try not to damage the roots too much. When I first got into live plants, I learned that my swords grew at a much faster rate and were visibly healthier when they were planted in the gravel.