Why are there blocked sums in my card?

[bg2015.atan]

For the first time I wanted to buy something in ebay so on 23.05.2015 I found a case for my phone that I wanted and decided to buy it. I don't have a paypal account so I selected the option to pay directly with my card. After I selected "pay" it gave me an error that the seller has changed his price and if I'm okay with the new price and I canceled it. On 25.05.2015 after consulting with the bank I find that there is 1$ block in my account from 23.05.2015. On 26.05.2015 I ordered the case from another seller and after paying and checking with the bank I find again block 1$ My question is why there is a block sum in my account and is it some kind of taxes? How can I unblock it ? For what purpose is it blocked ? And if it is somekind of tax why is it still block from the first time when there is no transaction?