BrickOwl doesn't collect/distribute sales tax on behalf of the seller; that's the individual seller's responsibility. When you open your store (if you haven't already), go to My Store>Settings>Tax. This is where you'll set up your tax rates (aka "tax profiles") by zip code.
You'll see some European tax rates already set up for you if you'll be selling to the EU.
You will need to collect sales tax for sales in your state. Then depending on volume and value of sales to other states, if you meet the threshold for other states (all different) you will need to collect and submit sales tax to those states. Other than Kansas it's unlikely. Also an aside, brick owl is a private uk based company. Uk and Eu are another more complex story
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You'll see some European tax rates already set up for you if you'll be selling to the EU.