The Amazon reviews can have a huge effect on your book sales. You need to be popular to become popular which can be tricky when you first make a book available.
You need to drive as many reviews to your book as possible so try to get your friends and family to do a review each. A minimum of 4 or 5 is really good but up to 10 is what you need.
The number of reviews a book has is a good indicator to a possible purchaser as to how serious they should consider it.
As a self publisher you have to take responsibility to make sure this section is populated which means promoting it in wherever you can. Unfortunately, a genuine review is usually only made when the customer either really loves it or really hates it.
Once you have got going with reviews you should be able to rely on your normal sales to get further reviews.