First order of business. Welcome to the wonderful world of Motor Bicycling and the Forum.
Second, The matter of needing to pedal is a two part answer. 1) the motor may need assistance going uphill depending on the size of sprocket you use The larger the sprocket the more torque (less Pedaling uphill but less top end speed) as with the smaller sprocket less torque (more pedaling with faster top end speed) So that part is a trade off. 2) The use of a Jack-shaft gives you the ability to use the gearing on the bike therefore giving you the larger and smaller gears However the trade off is expense.
her is a video showing just how a Jack-shaft works.....http://sickbikeparts.com/SBP%20Video3.wmv
Good Luck and once again Welcome. If you have questions you couldn't find a better place to ask them.