Getting started needs only a source, *.avs, script which you should already know how to create.  If your source and source input filter combination are not very seek friendly using FilmCutter's video editor is going to be a reasonably frustrating experience.  Open your script while in the script editor and then switch to the scene editor or from the scene editor use " File | Open Script File " in the main menu.

Find the first frame of your first scene and click to set the start frame.  Continue by navigating to the last frame of your first scene and click the button again which has switched to display the following.  Both the start frame and end frame number boxes have grayed and three buttons have enabled.

You have four choices at this point, cancel the scene, add the selected scene to the project, preview the scene defined or directly edit the frame start and end numbers by clicking the mouse in the start and end frame number boxes to re-enable them and pretty much change the numbers at will.

As you click the boxes the viewer will follow jumping to the frame number in the box you have clicked.  Advancing the frame counter changes the enabled box.  Your start and end frame numbers for your first scene are displayed in the boxes on the left, your may if you wish change the frame numbers pretty much at will.