My suggestion would be to go with Sinatra over Rails initially. You could potentially go with Node/Express instead, but picking up async javascript simultaneously may be a bit of a burden. Actually if you know Python, Flask may be the best place to start.
Picking up a heavyweight framework like Rails while simultaneously trying to understand web development is probably going to be very overwhelming. I'd only recommend jumping straight to Rails if you have significant experience with another similar Web Framework and understand at least the basics of Ruby.
Picking up a heavyweight framework like Rails while simultaneously trying to understand web development is probably going to be very overwhelming. I'd only recommend jumping straight to Rails if you have significant experience with another similar Web Framework and understand at least the basics of Ruby.