The @ sign is a shorthand for a couple of square brackets. For example
Line[Table[{n, n + 1}, {n, 1, 5}]]
can be slightly shortened to
Line@Table[{n, n + 1}, {n, 1, 5}]
When using the brackets there is the task of locating the exact end of the expression to embrace, which is error-prone in complicated code.
The @ usage is quite similar to the "\circ" notation that mathematicians use for the composition of functions.
