A lot of zoom objectives have the designation Macro. But these are not true macro objectives. A true macro objective has a ratio of 1:1, meaning your subject will appear as big on your sensor as it is in real life. The designation macro on a zoom objective is nothing more than saying you can get close to your subject and your picture will still be in focus.
Real macro objectives can focus from a very short distance from your subject. The most important aspect of a macro objective is the focal length.
Macro objectives usually start with a focal length of 40mm and goes up to 200mm. The bigger your focal length, the bigger the ditance to your subject can be to get a ratio of 1:1.
For stationary objects like flowers you can usually get by with a 50mm.
But if you are looking to photograph insects, you better buy at least a 90mm. This is because with 90mm, you can take the photo from a greater distance, without the insect getting startled.