Okay, so is there a shortcut to copy and paste every single layer's keyframe, that I have placed in a folder, from Frame 1 to Frame 2 ?
yes, select all the frames you want to copy. Press Mac: Command+c or Windows: Control + C. Select all the frames you want to paste to and press Mac: Command + V or Windows: Control + V. Bam!
Wait, copy every keyframe from 1 to 2? You mean you just want to move everything over one frame? Select the first frame and press F5.