Hey,
Here is how you can do it..
If you have your own website - Put the opt-in form on your site. One of the highest-converting locations for opt-in is the right sidebar.
But before people hand over their email address, you’re going to have to offer them something valuable in exchange. This could be a free eBook, discounts..
If you don't have a website and you are promoting affiliate products you can create landing page where you will collect email addresses. That means: don't send people directly to the affiliate offer. Send them first on your landing page, collect their email addresses, and then send them to the affiliate offer you're promoting.