The limits should be underscripts and overscripts of in normal input, and subscripts and superscripts when embedded in other text.
Product uses the standard Mathematica iteration specification.
The iteration variable is treated as local, effectively using Block.
If the range of a product is finite, is typically assigned a sequence of values, with being evaluated for each one.
In multiple products, the range of the outermost variable is given first.
The limits of a product need not be numbers. They can be Infinity or symbolic expressions.
If a product cannot be carried out explicitly by multiplying a finite number of terms, Product will attempt to find a symbolic result. In this case, is first evaluated symbolically.
Product can do essentially all products that are given in standard books of tables.