Just clock the "add to cart" button on the products you wish to buy. Choose the appropriate option from the drop down menu where appropriate. Then click on the view cart button at the top of the page and you'll be taken to Paypal's secure website where you can pay by your PayPal account or by credit/debit card.

Worldwide shipping is included and also paypal charges are included in the price

This is dependent on the country and all duties/local taxes incurred will be the buyer's responsibility.

Don't panic! Have a look again over your work. Look at the manual. Have a look on www.groupdiy.com at the support thread. This is a great forum specifically for audio- minded solderers! Take comfort in the fact that there's definitely a specific reason why it's not working... it's just about finding it! Definitely no magic or voodoo making it not work! No matter how much it feels like it!