Affiliate networks and programs (created by a single company) are typically super simple to join. It takes a few steps that can be accomplished in a few minutes, followed by a brief wait period. The larger stores may also require approval. But after that, any admin with access can conduct a search, grab a link, and insert it in a story or button.
Some networks have additional features, such as adding price comparisons between stores, live support, and useful reporting, but the most important factor is the relevance of the store to your niche content. Here is a list of the top networks, and how to find other programs that support your niche. Pleases join as a member to access this content.