What is Editing?

Editing
Is taking all pieces of individual footage and combining them together, so that it makes sense to the audience. It also involves adding sound effects, music and transitions, these will all help to make the film move on that bit more smoothly and in some cases will add tension, violence or horror.

Transitions
They are used to join two clips together, some are very simple but some are more advanced and can be used to show that some time has passed etc.
Dissolve - A gradual transition from one clip to another, they fade together. It could be used to show time passing.
Fade - A transition to a black or white screen then back to the same/different image. It may be used to show flashbacks, dreams or again, time passing etc.
Wipe - A new image will start to move across the original. This can show a new location or character, this was famously used in the original trilogy of Star Wars, every time a location changed.
Jump-cut - An abrupt cut from one shot to another. This can be used if a different charecter starts to speak or move.

Sound
Diegetic sound - Sound that is picked up during the filming process e.g Dialogue, footsteps etc.
Non-Diegetic sound - Sound that is added during the editing process e.g Music and other sound effects.