header.php

<nav class="navbar navbar-inverse navabar-fixed-top">
    <div class="container">
        <div class="navbar-header">
            <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#myNavbar">
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
            </button>
            <a href="index.php" class="navbar-brand">Worlds Store</a>
        </div>

        <div class="collapse navbar-collapse" id="myNavbar">
            <ul class="nav navbar-nav navbar-right">
                <?php
                    if(isset($_SESSION['email'])){
                ?>

                <li><a href="products.php">Product</a></li>
                <li><a href="cart.php"><span class="glyphicon glyphicon-shopping-cart"></span> Cart</a></li>
                <li><a href="settings.php"><span class="glyphicon glyphicon-cog"></span> Settings</a></li>
                <li><a href="logout.php"><span class="glyphicon glyphicon-log-out"></span> Logout</a></li>
                <?php
                    }else{
                            ?>
                <li><a href="products.php">Product</a></li>
                <li><a href="signup.php"><span class="glyphicon glyphicon-user"></span> Sign Up</a></li>
                <li><a href="login.php"><span class="glyphicon glyphicon-log-in"></span> Login</a></li>
                <?php
                    }
                ?>

            </ul>
        </div>
    </div>
</nav>