put them into horizontal lists. Preview Website
<html>
<body>
<style>
li {
float: left;
list-style-type:none;
}
</style>
<ul>
<li><a href="#">Contact</a> |</li>
<li><a href="#">Home</a> |</li>
<li><a href="#">SignUp</a></li>
</ul>
</body>
</html>
to correct yours...
<!-- change style to include header -->
<style>
body,h1,h2,h3,h4,h5,h6 {font-family: "Source Serif Pro", sans-serif}
header {float:left; list-style-type:none;}
</style>
If you want multiple lists, make multiple lists in columns. Nobody says you can't float and use tables.