There are tons of stand-alone lessons at BassEducation. Videos are organized by category and run from bite-sized 5–10min videos all the way up to 45min clinics on one specific topic.
I would suggest that most players start by checking out the Fundamentals Module or the Walking Bass Module (Modules can also be found in the navigation menu).
As you start to have specific questions or get an idea of something you want to explore further, you can peruse the various sections of stand-alone lessons below.
As always, make use of access to me and the rest of the Community by asking questions — I’m in there daily and always respond to anything asked of the community!