This is a variable declaration:
var a int
It says a is an int. That means a can contain any value that has the type int. Typical int would be like 0, 1, 2, and so on and so forth. It may seem odd to read the previous sentence, but typically is used correctly. All values of type int are typically int.
This is a variable declaration, followed by putting a value into the variable:
s := "Hello World"
Here, we're saying, define s as a string, and let the value be "Hello World". The := syntax can only be used within a function body. The main reason for this is not to cause the programmer to have to type var s string = "Hello World".
A note about the use of variables: variables in Go should be thought of as buckets with a name on them, ...
