I want to upload movies to YouTube from my Picasa account - without being forced to join Google+. The channel creation has a box to check saying you understand the changes this will make to your Picasa account, but doesn't explain if you will lose Picasa and be automatically forced into G+.
Picasa - A photo storage service from Google (also an application by Google) Google+ - The social network from Google
Both Picasa and Google+ are from Google, and to make it easy to manage Google accounts, Google is now integrating Google+ with most of their products and Picasa is one of them.
I suggest you to switch to G+, it has more features and all your products will be managed from one single profile (your G+ profile). Try it, G+ is better.