In the Merge Video dialog, you will see the list of selected files. You can manage this list using the available buttons:
On the right side of the dialog, a video preview is available allowing you to see how the merged video will look. Below the file list, the total duration or final time of the merged video is displayed in H:MM:SS format.
To merge the selected videos, click the "Merge" button. The merged video will be saved in the selected output format and stored in the output folder specified in the main application. If you decide not to proceed, click the "Cancel" button to close the dialog without merging the videos.