Email, call, whatever you like.
I simply emailed my order, along with the credit card number and expirey date split over 3 emails, (for security reasons).
Frederick from singa hobby was most helpful, and my package arived at my door in PC, 4 days after I ordered.
Your credit card company will convert the currency for you.
Ie Singa hobby will charge the amount due in Singapore currency, and your credit card company will convert at the current exchange rate, and then charge you in your currency.