Interaction design looks at the human factors and psychology that influence why people make certain decisions and how to encourage (or discourage) these decisions.

Components of interaction design can be:

Words

Using the right words can make an interface a lot easier to use. A button with the text Save File is clear in what its purpose is.

Visual elements

Using the right colours, shapes and fonts has a large impact on how easy a user interface is to use. A green quit button doesn’t assist the user.

Physical objects and space

Where items are placed on a webpage, application or game can impact the user experience.

People read from the top left so important information such as the title should be there.

For a video games users are often looking at the centre of the screen for the play area but other information is displayed around this.

Loading bars are often in the centre or bottom right.

Time

By indicating the time that tasks will take or having loading bars is makes it easier for the user to understand what the system is doing.

Behaviour

Different systems and outcomes require different ways of interacting with them.

A physical button that makes a sound informs the user that it has been pressed. The click sound of a keyboard or mouse does the same.

Even the loading … to indicate that a program is loading indicates a behaviour to the user.