Dude, if you have individual problems were happy to help. But
Nobody is going to walk you through this completely..but I'll give it a shot
First, does it run? Regardless your going to rebuild the engine. The seals are 40years old and need replacing....Soo tools, bearings, seals, gaskets. Possibly new crank cylinder and Piston. Before you start, does the engine spin over? If Soo clean the carb and check for spark. If no spark get acquainted with electrical trouble shooting. If it runs, you can proceed, of not. Think about wether you want the project or of it's too big to take on with your knowledge.
Then, brakes, tires, bulbs, paint, cables...is the tank leaky? If Soo a new one will probably cost more than what the whole bike is worth.
The engine appears to be a 505/1a. So the underpowered 30mph version. The d is the better variant, 30mph but alot more power. Easily will hit 40 with mild mods...if you want it faster, your gonna want to do the mods while you have it apart. You can switch out a d crank n jug easily.
Edit, diddnt see that it was a b. Your gonna want to change that.lol (edited)