Don’t put all the content of a post at the beginning of the site

Question

I’m making a site posts... and I’m having difficulties to set up how many letters can have at the beginning of my site... because the button itself I already have but I wonder how can "Set" up how many letters can have in the post... is currently like this on my website: http://prntscr.com/jb35jk When you open the site appears ALL the content of the post I did but it is not cool to leave all the text at the beginning because then the "Continue reading" button would be useless! My code looks like this: my text appears with the variable "$descricao"

<div class="">
    <?php
        if(isset($_GET['posts'])){
            $pg = (int)$_GET['posts'];
        }else{
            $pg = 1;
        }

        $maximo = 2;
        $inicio = ($pg * $maximo) - $maximo;

        $seleciona = mysql_query("SELECT * FROM posts ORDER BY id DESC LIMIT $inicio, $maximo");
        $conta = mysql_num_rows($seleciona);

        if($conta <= 0){
            echo "<code>Nenhuma nova notícia foi declarada! que pena :/";
        }else{
            while($row = mysql_fetch_array($seleciona)){
            $id = $row['id'];
            $titulo = $row['titulo'];
            $descricao = $row['descricao'];
            $imagem = $row['imagem'];
            $data = $row['data'];
            $hora = $row['hora'];
            $postador = $row['postador'];
            $sql = "SELECT * FROM usuarios WHERE usuario = '$postador'";
            $query = mysql_query($sql);
            $linha = mysql_fetch_assoc($query);


    ?>

    <div id="panel" align="left" style="color: #000;">
        <p><a href="?pagina=post&id=<?php echo $id;?>" class="titulo"><?php echo $titulo;?></a></p>

        <?php if($descricao != null){?><p class="descricao"><?php echo $descricao;?></p><? }?>

                <a href="?pagina=post&id=<?php echo $id;?>" class="lermais">Continuar lendo</a>
                <br>
                <br>

        <?php if($imagem != null){?><p><img src="<?php echo $imagem;?>" class="foto"/></p><? }?>

        <span class="glyphicon glyphicon-user" aria-hidden="true"></span> Postado por: <?php echo $linha['nome'];?> <img src="https://minotar.net/avatar/<?php echo $postador?>/20"></p>

        <p><span class="glyphicon glyphicon-time" aria-hidden="true"></span> Postado em: <?php echo $data." às ".$hora;?></p></br>

    </div>

    <?php }}?> 
</div>

<nav align="center">
    <ul class="pagination">
        <?php
        $seleciona = mysql_query("SELECT * FROM posts");
        $totalPosts = mysql_num_rows($seleciona);

        $pags = ceil($totalPosts/$maximo);
        $links = 2;

        echo '<li><a href="?pagina=inicio&posts=1" aria-label="Página Inicial"><span aria-hidde="true">&laquo;</span></a></li>';


        for($i = $pg - $links; $i <= $pg -1; $i++){
                if($i <= 0){}else{
            echo '<li><a href="?pagina=inicio&posts='.$i.'">'.$i.'</a></li>';
        } 
    }

        echo '<li><a href="?pagina=inicio&posts='.$pg.'">'.$pg.'</a></li>';

        for($i = $pg + 1; $i <= $pg + $links; $i++)
            if($i > $pags){}else{
            echo '<li><a href="?pagina=inicio&posts='.$i.'">'.$i.'</a></li>';
            }

            echo '<li><a href="?pagina=inicio&posts='.$pags.'" aria-label="Última página"><span aria-hidde="true">&raquo;</span></a></li>';
        ?>
    </ul>
</nav>