Import taxes

I've recently ordered a few items from UK and am baffled by how the Spanish taxes are applied .

For 1 item I had to pay approx 40% of the item purchase.

For a few smaller items from UK...no tax was added.

For a small item just yesterday...approx 20% of item purchase.

I assume if I order from Amazon.es there will be no tax charged, as this was the case when I ordered a few items from there.

Also, if a larger item comes from the UK, is it automatically delivered meaning a delivery charge plus import tax?