The string concatination operator '+' requires that both operands be of type string. If one is a string and the other is not than the string may be coerced to a non string and the arithmetic 'add' operation performed. This depends on the type and position of the non string operand. See type coercion for more details
The string concatination operator will build a new string consisting of the first string followed immediately by the second.
e.g.
A = "hello"
B = "world"
C = A + Bwould set C to the string "helloworld" e.g.
A = "hello"
B = 27
C = A + Bwould set C to the string "hello27" e.g.
A = 27
B = "world"
C = A + Bwould set C to the integer 27 e.g.
A = 27
B = "world"
C = $A + Bwould set C to the string "27world"