Every person who has AIDS has HIV, but not every person with HIV will develop AIDS. Because there are now lots of treatment options available for people living with HIV, far fewer people are developing AIDS. Often, those that do develop AIDS are people who have not been tested for HIV and have never taken treatment. Once started on HIV treatment, death due to AIDS can be prevented.
The only way to find out if you have HIV is to get tested for the virus. There is no test for AIDS as it is a collection of infections and illnesses that occur because of untreated HIV infection. Often, people can experience a range of them before HIV is discovered to be the cause. This is why AIDS is sometimes difficult to diagnose.
Ultimately, HIV is a virus that attacks the immune system and AIDS is a term that can only be used when HIV has caused severe damage to the immune system.