Transitions and effects are used in videos to manipulate time , for example to go back into time and go into the future. this would not be possible without transitions. you would use transitions such as the fade or wipe when you want to cut into another scene in a different location. Also when going back into time or the future you would use a fade or wipe also.
Also you would a graphic math. a graphic match is when you match two things together, an famous example in a film scene where this is used is 'Psycho', in which the a plug hole with an eye .
Furthermore you could follow the action is which you would follow the action that a person is doing in the scene to see everything they are doing, especially with movement, an good example of this used in a ilm is in 'Mr&Mrs. smith' in a scenes where there is a gun fight in a shopping market in which it follows where they shoot and who they shoot.
Multiple points of view can also be used, this will allow the audience to get everyone's perspectives in the scene, and will allow sometimes to get what a certain person's view is compared to another which can be sometimes both good and bad.
Shot variation is also used in movies, this is different shots in the same scene and will often differ from using close ups and long distance shots. An example of where this is used in the film 'Matrix' where neo is being shot at and the shot will change from when the bullets are shot form a long distance to a close up shot of him dodging them, showing good shot variation
Finally the use of manipulation of time and space is used, which allows the audience to realise when the film is going back into time by using certain transitions. An example of this in a film would be in 'The Wizard of Oz ' where the colour is changed to represent going back into the past.
in my film i have used many of the above to manipulate both space and time. in my i used a transition and effect to go back into time and jump into present, this is shown as when gone into the past the scene is in black and white and i also use a sound when i am manipulating time to show the audience clearly that this is happening, we use this when 2 people are sitting in the car and one of them have realised thy have left their phone somewhere and have go into the past to remember where it is and go to get it.. i also used the shot variation in a scene when the two people are walking into a room and have to use a card to scan to get in and we had zoomed in on this action, which is shown in the video below.