There are four basic elements for programming in Scratch:
Sprites are the objects that perform actions in a project. These may be characters, objects, or items to be manipulated. A costume of a sprite is one out of possibly many appearances of a sprite. Sprites may change their look to any of available costumes. The panda that you see in the figure is called a sprite. Sprites understand and obey sets of instructions that you give them. Many of the applications you’ll create in SCRATCH will contain multiple sprites, and you’ll use blocks to make sprites move.
The stage is a background or a “back-drop” for your project. In the figure, it is represented by the white background. You can paint, import, or take a photo as your background. The Stage is where your sprites move, draw, and interact. The Stage has its own set of scripts, images, and sounds.
Attributes of the sprite and the stage can be manipulated using a script or set of instructions. A script consists of a set of blocks that fit together like a jigsaw. When you run a script, it executes every block sequentially from top to bottom. For a sprite, you can make multiple scripts which can run at the same time simultaneously. A script is basically used for controlling the actions of one or more sprites.
Blocks are puzzle-shaped shapes that are used to create code in Scratch. As said above, the blocks fit together like a jigsaw puzzle where each data type (event, command, reported value, reported Boolean, or script end) has its own shape and a specially shaped slot for it to be inserted into – eliminating the typing errors that tend to occur when people use text-based programming languages. A series of connected blocks form scripts.
The block palette (indicated in the figure) is an area of the graphical user interface located between the stage and sprite pane and scripting area. It is here that categories of blocks are color-coded and can be clicked to bring up a new set of blocks that can be dragged into the scripting area to program a sprite or the stage. The blocks are located underneath the block categories, and if they overflow the page vertically a scroll bar will be present that does not scroll the block categories but only the blocks themselves.