Welcome to the forums,
The
Red Line is showing you the
Preview Range. To learn about this you can refer to the User Guide page# 40.
To remove it press the
Project above
Clip located beneath the preview window. Then place the playhead at the beginning of your project, and then press the Mark-In
[ button. Next move the playhead to the end of your project and press the Mark-out
] button.
Instead of using the Mark-In/Out buttons, in Project Mode, slide the small triangles beneath the preview window fully to the beginning and end.
You can also use the keyboard shortcuts of
F3 for
Mark-In and
F4 for
Mark-Out.