Understand the idea of staring an Amazon business with less than $500 will start out very slow and needs to be looked at as a long play. But, getting started now with little money is a whole lot better than never starting at all!
First
You need to start your Amazon store. Be prepared to pay $39/month. Setting it up is pretty simple. There are a lot of YouTube videos showing this process if you need help.
Next
Use the tools provided by Amazon to help you search by category to find the most trending items in each category. Write down the top 10 most trending items that you like. Preferably these items should be lower ticket items ranging between $10 and $30. Use an app like Amzme to search the back end of Amazon to see how many people are selling those items and see the total amount of sales in the last 30 days.
You found the item you want to start with
After searching you pick just one of those items you like the most. Now search aliexpress, dhgate, Alibaba and other sites like these to find your supplier. You can buy one to check the quality of you want.
FBA
Once you have chosen your item you need to set up your fulfillment by Amazon (FBA) account. This will make it to where you can have your items sent directly to Amazon's warehouses for them to fulfill your orders for you. It is the most cost effective also because you won't have to worry about paying for packing materials or shipping upfront.
Make your first order
Purchase as many as you can with your limited budget. If you can only order a couple that is fine. You have to start somewhere. The idea is that once you sell these you can use the money you make to order twice as much next time. Have them shipped to Amazon FBA.
There are several other things you can do to help grow faster but they all require more money. An example of these things include Amazon marketing, Facebook marketing, review clubs, free samples, or social media influencer marketing.
This is a rough walk through but gives you a basic understanding of the basic steps to get started on Amazon. If you have any specific questions let me know.