Create a simple plugin that allows link entered in admin side to be used in button on website -- 2

I need a plugin created that will allow for a link to be entered into a field on an admin page and that become the target link for a button within website. Let me explain clearer: On this webpage there is a button that says "click here": [login to view URL] This page was built a plugin called Instabuilder. Refer to screenshotS to see how the target link is assigned to that button. I need their to be an admin page that allows me to enter the link int a field and save it. That link will become the target link for the button on the page: [login to view URL] In Summary, I need a plugin built that has 1 admin page. When I go to that admin page there sbould be 1 field. In that field an admin can paste a link and click save. For example let's say that [login to view URL] was entered and saved in the field. Now the button on page [login to view URL] should target the link http://www.abc.com.