Braces allow me to lump pieces of program together. Such a lump of program is often called a block . A block can contain the declaration of variable used within it, followed by a sequence of program statements which are executed in order. In this case the braces enclose the working parts of the function main . Notably it will read in values for the width and height of the windows and then calculate and print values for the glass area and wood length.
C calls the place where values are put variables.
At the beginning of any block you can tell C that you want to reserve some space to hold some data values. Each item you can hold a particular kind of value. You declare some variables of a particular type by giving the type of the data, followed by a list of the names you want the variables to have. This is a list. A list of items in C is separated by the , character.