Shipping by Weight
Let's say you live in the US ...
If you want to figure shipping rates based on zone, you can set zone 1 to be US ... zone 2 to be Canada, and zone 3 to be all other countries.
Go to Admin / Modules / Shipping
Click on Zone Shipping and click edit.
Zone 1 will be US - create a table (or set of rules) for the shipping costs.
Let's say everything up to 3 pounds will cost $5.00 to ship - it will look like this: 3:5.00
You can have increments of whatever you choose .... up to 5 pounds would cost $7.00 (5:7.00), up to 8 pounds would cost $10.00 (8:10.00), etc., etc. You keep setting these rules until you get to the largest possible weight you are willing to ship.
Be sure to click "update" when you are finished.