What a notice of opposition means
A notice of opposition is filed with the Trademark Office by a third party who wants to stop your application from being registered. In many cases, the opposing party believes your mark infringes on theirs.
Your next steps
An opposition does not mean your trademark is lost. It does mean that you have to defend the application if you want registration to move forward. Consider working with a trademark service such as Marcaria.com, or with a trademark attorney who is familiar with the laws where your application was filed.
Whoever represents you must submit your defense before the deadline set by the Trademark Office.