While each person's experience will vary, hearing aids may allow a person to experience certain sounds they had never heard before (or at least for some time). Relearning takes place in the central auditory nervous system and not in the ear itself.
Recent experiments suggest that a listener's ability to comprehend speech may continue to increase over a period of several months when wearing a new amplification system. This process is termed acclimatization. Most dispensing audiologists currently allow for a trial or adjustment period with new hearing aids.
It is important to understand that the sound you first hear from your new hearing aid will not be the same experience that you have 30 days or longer. As the central auditory system relearns how to listen to sound, your hearing will improve. This acclimatization process is very important and must be given time for you to adjust and enjoy your new hearing capabilities.
Not sure what to expect from your new hearing aids? Read this post on What to Expect with New Hearing Aids.