By default the "Edit" icon is grayed out. To activate the Edit menu, you have to select an item first. When a chapter is selected, you can click the “Edit” icon on the tool bar of main interface to edit selected file.
In Video Editor there are six edit tabs: Trim, Crop, Text Watermark, Image/Video Watermark, Effect, and Audio Replace.
Trim: Cut selected video to remain desired duration only.
Crop: Cut off the black edges of the image and set the aspect ratio.
Text Watermark: Add text watermark to selected video clip.
Image/Video Watermark: Add image or video watermark to selected video file.
Effect: Adjust the brightness, contrast of the video, and the volume of the audio.
Audio Replace: Replace the original audio track with favorable music.