How can I Clone a Schedule in TimeTabler ?

The advantages of cloning, and the way of doing it, are described in Section H27 in your Manual.
Here is a summary of the steps:

To make a Clone, go to the List of Schedules Screen.
At the bottom of that screen is the 'Clone' button (to clone the schedule that you have selected / highlighted).

It gives you the choice to:
-- 1) Keep all the lessons in the Clone, assigned in the same periods as in the original schedule.  ie. the Clone is identical to the original.
or
-- 2) In the Clone, unassign all the previously-assigned lessons, so that you can then re-assign them from scratch.

1 is the usual choice.

It is particularly useful to make a Clone or many Clones [all of type 1] just after you have assigned all your Fixed Points.
So then you have several copies of the basic timetable, ready to start some 'What if...?' investigations [without having to repeatedly re-assign the Fixed Points].

There are more details if you click the Help button on this List of Schedules Screen.