I’m not in Vine, that’s invitation only.
All you have to do is post reviews on Amazon. If you are into subscription boxes, you probably already have a lot of things around the house you can review. Write good, thoughtful, detailed reviews (good does not always mean positive — if some mascara makes your eyes burn, it does not deserve a high star rating…).
The only requirement for posting a review is that you have an account with which you have made at least one purchase.
Anyway, if your reviews actually are helpful to people, you will get votes on them and your reviewer rank will start to increase. Be sure to put an email address in your profile. It may take a few months or a year, but you will start to get offers from outside vendors to review things.
The only warnings are:
(1) If you get something for free or a reduced cost for review (including a coupon code), you have to say so. (Like how Liz indicates if a box was sent by a company for review.)
(2) There are some clubs that give Amazon coupon codes. A lot of them show up on Facebook. Don’t join those. A lot of people have had their reviewing privileges revoked for being part of those clubs. Only accept coupon codes directly from vendors.