To keep your patent valid, you will need to pay a fee each year. You must also make sure your details are registered correctly. If someone violates your patent, you can take action. You can keep your patent yourself, or you can sell or license it to someone else.
If you own a patent, it is possible to file a patent on the same invention in a different country. You must do so within 12 months of the application date. You will no longer be able to do this once this 12-month period has ended (priority right under the Paris Convention).