You've downloaded and installed TubePress to your website. Great! If this is your first time using TubePress, you'll need to perform some initial configuration before you go further. These are one-time jobs that should take just a few minutes.
First, you'll want to find the TubePress options page within your WordPress admin dashboard. This page is located
WP Admin > Settings > TubePress. Go ahead and navigate there now before moving on.
TubePress needs to regularly communicate with video providers (YouTube, Vimeo, etc) on your behalf. To sort out all the incoming requests, and for quota purposes, these providers mandate that everyone supplies "API credentials" with each message. It's the rough equivalent of showing someone an ID card before you have a conversation.
Setting up your API credentials is easy, free, and should take less than 5 minutes per provider. You only need to complete this step for providers that you actually use. e.g. if you aren't using Vimeo, you can safely skip the Vimeo API setup.