Even though they’re a behemoth – which might be an understatement, I’m only classifying Amazon Associates as a notable mention. They’re not really my favorite because I’m a bit cautious about Amazon’s business practices. I see them as a ruthless company that will do whatever it takes to cut costs, and I foresee that they will progressively reduce their affiliate commissions as they grow larger. Hence, I wouldn’t build my affiliate strategy and offerings around what Amazon has to offer.
Remember - don’t come off as the guy or gal that has spent the last month looking for ways how to start affiliate marketing and is now desperate for clicks. That will get you nowhere. Instead, be helpful - actually interact with people and try to help them when you can, and if you see a great opportunity to post your affiliate link - do it. Otherwise, you’ll just get banned for spamming.

You can still ask for samples before you become an affiliate. Or, you can use a trial feature before using any paid tool or subscription. I would still recommend investing money in trying out the products yourself.
An affiliate network acts as a sort of middleman between you and merchants (the companies selling the products you're marketing). As a beginner affiliate, an affiliate network is beneficial because it is easier to get used to, and it provides tools that you can use to track your earnings and performance.