First, in Javascript, you need to target #Sign-Up and NOT #Sign-Up-Group because it does not exist in your HTML.
Second, in HTML, you need to open parentheses when you call a function on click

HTML change:

<button class="Sign-Up-Button" id="Sign-Up-Button" onclick="revealSignup()"></button>

Javascript change:

document.getElementById("Sign-Up").style.display = 'block';

right now am trying to make a sign up page for my website currently i have a signup button and some javascript that should be connecting to it so the signup page itself appears

html:

 <button class="Sign-Up-Button" id="Sign-Up-Button" onclick="revealSignup"></button>

   <div class="Signing-up" id="Sign-Up">
    <form action="results.html" method="GET">
        <div>
        <label>Name</label>
            <input>
            </div>
        <div>
        <label>Password</label>
             <input>
      </div>
      </form>
      <button id="Sumbit-End">Sumbit</button>
      </div>
      

css:

 .Sign-Up-Button{
   background-color: #0099ff;
   position: absolute;
   text-align: center;
   font-family: monospace;
   font-size: 25px;
   border-radius: 15px;
   color: white;
   height: 50px;
   width: 105px;
 }
    
    
    .Signing-up {
    position: absolute;
    top: 370px;
    left: 850px;
        background-color: white;
        z-index: 1; 
        display: none;
    }

Java script:

function revealSignup(){
    document.getElementById("Sign-Up-Group").style.display = 'block';
}