First you should go to site you want to buy something then go to the menu where you can deposit bitcoin, it redirected me to some bitpay.com page with a qr code, so I copied the address besides the qrcode, and went to webmoney's WMX purse and pressed spend (or send bitcoin) and it successfully been sent, but bitpay didn't recognized the payment so after few days I got the transaction from webmoney and blockchain (supposedly the site they use for bitcoin transferring) and sent it to the purchase site support and asked them for help after few days they added it to my account.
Have you tried looking at your Webmoney Bitcoin purse's FAQ, for "how to send money"? – Murch – 2013-11-24T10:29:16.607
I finally did it with many complications. – for-a-fistful-of-BITCOIN – 2013-11-24T11:07:46.973
1Then it would be nice if you answered your own question, so that other people that find it can benefit from your effort. – Murch – 2013-11-24T15:07:22.497