PLR (Private Label Rights) products are pre written content that you buy and can use any way you want.
PLR is given along with a license that tells you what you can and cannot do with this package: edit it, publish it, put your name, create products from it, etc.
When offering PLR products as a free gift, it is important to ensure these products are labelled with "giveaway rights".
We highly recommend you to read license before to buy any.
Moreover, if it's the text you are after, do not hesitate to search Google for sections of the text, to see if and how much this package is already on the web.
We also recommend you edit the content you buy, as (depending on the quality) some of them can be quite poor (bad syntax, etc.).
Regarding how to source quality products to sell and quality copywriting for emails, we would always advise the sites ClickBank and JVZoo in the first instance.
It is important to find products that you feel confident with and which do not compromise the integrity or values of your business/company.
Once you have selected two or three products, we would advise you to directly contact the affiliate managers of the products that you like and ask them which of their ads, sales pages, email copy have the most success.