To open a new file- flie import- change footage to composition- the layer sizes one not just composition. . Open. To set the duration- composition settings- then go down to DURATION and change the times e.g. 0.00. 15.00 Hold down Y for vertical movement and click and drag when key framed. Copy and pasting key frames. Select blue diamonds and layer- cmd V This tool converts movements into vector shapes when you draw with it.
A hold key frame keep the key frame locked untill another key frame is created. Helps to achieve a a solid keyframe movement. Can be used for fading in and out. Changing opacity as well though.