Fixing Your Lines
Often, your lines will not look like you planned. Rather than starting over, just fix your lines as necessary!
To close a path, use the Pen tool. First select one of the two points you want to join, then select the other point. When you are hovering over the first point, the Pen tool will have a slash next to it. When you are hovering over the second point, it will have an "O" next to it.
If you wish to change a point from a smooth point to a corner point, just click on the Convert Anchor Point button in the Control palette and click on the point you want changed. Doing so will convert the selected anchor point to the opposite point type.
Adding or Removing Points
To add or remove a point on a path, just select the Pen tool with a plus sign (to add) or minus sign (to subtract) next to it and click where you want the point added or removed.
For a challenge, try recreating the following outline using only the Pen tool and the Add Point, Subtract Point, and Convert Point tools mentioned above.