How to create a certificate X509 Certificate

Question

I am following a video tutorial for WCF web services in that he is using&nbsp;<h1 style=" 0px; 0px; font-weight: normal; font-size: 24px; display: table-cell; vertical-align: top; 823.333px; color: #222222; word-wrap: break-word; font-family: Roboto, arial, sans-serif; background: #ffffff;"><span id="eow-title" dir="ltr" title="Create Your Own Self Signed X509 Certificate" style=" 0px; 0px; font-size: 24px; background: transparent;">X509 Certificate ,how to create that for my app</span></h1>