Generally, micro means shooting at greater than 1:1 magnification, while macro is anything up to 1:1. In Nikon's parlance, "micro" meant lenses capable of 1:2 or higher in the manual focus world, or 1:1 in the AF world. "Macro" is a term they attach lenses capable of at least 1:4.
Your 70-300 is capable of 1:3.9 so it has a "macro" mode.
There are many ways to take macro photos: - close-up filter attachments such as Nikon No.'s 0, 1, 2, 3, 3T, 4T, 5T, or 6T - extension tubes such as PK-11A, PK-12, PK-13 and PN-11 - reversing rings such as BR-2A and BR-5 - bellows - "micro" lenses that achieve 1:1 by themselves