This is probably a really simple thing to do, but I can't figure it out and
can't find it in the help anywhere.

I have a worksheet that has rows of data. I periodically enter more rows as
time goes on. I'd like to be able to write a formula that summarizes data
from a certain column. The formula is easy to figure out, but I can't figure
out how to refer to the entire column, and not just a range of cells in the
column.

For instance, I can say "=SUM(B3:B10)", but when I add data to row 11, my
formula will need to be updated. I could just pick a really high number (like
"B3:B1000"), but I may eventually get that many rows, and I don't want to
have to remember to check that my formula range is right. How can I say, "sum
all the data in all non-empty rows in column B underneath row 3?"

Thank you!