IN the PHP File the Brand value is Showing but when I trying to get it through another page it return NULL.
Page1 PHP
<div class="col-md-6">
<div class="row vertical-divider-page3">
<div class="col-md-4">
<div class="page3-img">
<img src="<?php echo $value["Image"]; ?>" class="img-responsive" id="custompage">
</div>
</div>
<div class="col-md-8">
<div class="page4">
<a href="product.php?post=Reference&value=$value"> <h3 id="custompage"><?php echo $value["Brand"]; ?><span><br><?php echo $value["Reference"]; ?></span></h3></a>
</div>
</div>
</div>
</div>
Product Page
It looks like you were trying to pass $value into your url which won't work for two reasons.
You didn't echo this value in PHP so you're literally just passing the string $value. Looks like you're trying to pass the 'Brand' along so you'll need to make sure your url query parameter is 'Brand=$value["Brand"]' and not just $value.
$value is an array and you cannot pass an array into the url like you are trying to do.
<a href="product.php?post=Reference&Brand=<?php echo $value["Brand"]; ?>"> <h3 id="custompage"><?php echo $value["Brand"]; ?><span><br><?php echo $value["Reference"]; ?></span></h3></a>