The db function is the low level procedural interface to the database. You'll have to specify points, layer, width etc as arguments to the function.
The leHi function includes the user interface (Hi stands for Human Interface), and will prompt you to click on points, and an options form will specify the width.
There are a number of non-Hi le functions, but these typically provide higher level capabilities than db functions.
Db functions can be used in pcells, whereas le functions should not.