Inserting new drill bit

Assuming that it is this drill:

http://www.toolpartsdirect.com/cgi-bin/schematic.cgi/blackdecker/7144-04_TYPE_4

You will need a chuck key - hopefully you have that with the drill. It's a little t-shaped bar with a cog on one end. You put it into the holes in the chuck (the part at the end which grps the bit) and turn anti-clockwise to open the jaws. Place a bit in the centre and then turn it clockwise to tighten. Tighten the bit using each of the three holes in the chuck and make sure you remove the chuck key before you use the drill - keep it safe!