How to use the symbols +=, *=,-= 
<p>These operands may be simple but the difficulty of finding explanations which are definitive and complete prompted me to ask. What are the character combinations containing an operand followed by an equal sign (such as *=, -=,+=, etc), what do they do and how are they useful (especially pertaining to non-numeric fields)? </p>

<p>Examples as well as definitions would be greatly appreciated.</p>

<p>Thanks</p>
