I've read a lot of different things, so I'm wondering, if I have a web site and a physical location in California, do I have to now charge web site visitors a sales tax if they purchase a web site subscription service from me, for services I provide?
You will have to charge sales tax for residents in California. If you have a physical presence in any other states (like an office or warehouse), you will have to charge sales tax for the residents of those states as well.
However--this only applies for physical/tangible goods. For a digital good or service, like a digital download or subscription to access content, there's no sales tax.
That said, I'm neither a lawyer nor an accountant, so you should check with one or both to verify that this is the case in your state and county.