Adobe Acrobat Pro DC 2015 - Add signature to document

Hi

I just installed Adobe and never really used it before but finding it extremely complicated to add a signature to a PDF document. I have followed this video to successfully create the signature How do I add a scanned signature to a digital signature? | Acrobat X Tips & Tricks | Adobe TV

After successfully creating the signature now I'm stuck i do not know how to add this to a newly opened PDF document. I seen videos to add to Adobe 10 but I am on the newer version - the same version as in the video I followed above. If I click Fill and sign and click it opens a text box??

Help appreciated.

Thank you.