It depends on how your data is populated in column B. You could
instruct Excel to evaluate each cell until a blank cell is encountered
(if the data is contiguous), or run for a given number of repetitions.

Here's an example of code that starts at cell B3, moves down a cell and
evaluates the entry in that cell, and stops when it encounters a cell
with the value "stop".

sub Evaluate_Column_B
range("b3").select
do until activecell.value = "stop"
{{{your process here}}}
activecell.offset(1,0).select
loop
end sub