Simple statement is an expression terminated by semicolon.

For example:

integer MyVariable;

Block of statements is a series of simple statements (each of them is terminated by semicolon). The statements in a block can follow each other in one line or they can be written in more lines. They are surrounded by curled braces. No semicolon is used after the closing curled brace.

For example:

while (MyInteger<100) { 
    Sum = Sum + MyInteger;
    MyInteger++;    
}