Be sure that when you draw the line, you click on the tool, then click and hold down. Move the mouse to create the line, then release the mouse when you're done. Also, select the line once it's drawn and increase the width with the line width field on the toolbar, a little left of center.
There isn't an Erase feature but if you want to get rid of anything, just click on the object and press the Delete key on your keyboard.
This was first published in May 2006