Inside Admin_area folder ,Make one page - insert_product.php and make folder includes then store page - db.php
<!Doctype HTML>
<head><script src="//cdn.tinymce.com/4/tinymce.min.js"></script>
<script>tinymce.init({ selector:'textarea' });</script></head>
<body bgcolor="#999999">
<?php include("includes/db.php");?>
<form method="post" action="insert_product.php" enctype="multipart/form-data">
<table width="700" align="center" border="1" bgcolor="#3399CC">
<tr align="center"><td colspan="2"><h1>Insert New Product:</h1></td></tr>
<tr><td><td align="right"><b>Product Title</b></td><input type="text" name="product_title" size="50"/></td></tr>
<tr><td><td align="right"><b>Product Category</b></td>
<select name="product_cart">
<option>Select a category</option><?php
$get_cats="select * from categories";
$run_cats=mysqli_query($con,$get_cats);
while($row_cats=mysqli_fetch_array($run_cats)){
$cat_id=$row_cats['cat_id'];
$cat_title=$row_cats['cat_title'];
echo"<option value='$cat_id'>$cat_title</option>";
} ?></td></tr>
<tr><td><td><b>Product Brand</b></td><select name="product_brand"><option>Select Brand</option><?php
$get_brands="select * from brands";
$run_brands=mysqli_query($con,$get_brands);
while($row_brands=mysqli_fetch_array($run_brands)){
$brand_id=$row_brands['brand_id'];
$brand_title=$row_brands['brand_title'];
echo"<option value='$brand_id'>$brand_title</option>";
} ?>
</td></tr>
<tr><td><td align="right"><b>Product Image1</b></td><input type="file" name="product_img1"/></td></tr>
<tr><td><td align="right"><b>Product Image2</b></td><input type="file" name="product_img2"/></td></tr>
<tr><td><td align="right"><b>Product Image3</b></td><input type="file" name="product_img3"/></td></tr>
<tr><td><td align="right"><b>Product Description</b></td><textarea name="product_desc" cols="35" rows="10"/></textarea></td></tr>
<tr><td><td align="right"><b>Product Keywords</b></td><input type="text" name="product_keywords"size="50"/></td></tr>
<tr><td><td align="right"><b>Product Price</b></td><input type="text" name="product_price"/></td></tr>
<tr align="center"><td colspan="2"><input type="submit" name="submit" value="submit"/></td></tr>
</table>
</form>
</body>
</html>
<!Doctype HTML>
<head><script src="//cdn.tinymce.com/4/tinymce.min.js"></script>
<script>tinymce.init({ selector:'textarea' });</script></head>
<body bgcolor="#999999">
<?php include("includes/db.php");?>
<form method="post" action="insert_product.php" enctype="multipart/form-data">
<table width="700" align="center" border="1" bgcolor="#3399CC">
<tr align="center"><td colspan="2"><h1>Insert New Product:</h1></td></tr>
<tr><td><td align="right"><b>Product Title</b></td><input type="text" name="product_title" size="50"/></td></tr>
<tr><td><td align="right"><b>Product Category</b></td>
<select name="product_cart">
<option>Select a category</option><?php
$get_cats="select * from categories";
$run_cats=mysqli_query($con,$get_cats);
while($row_cats=mysqli_fetch_array($run_cats)){
$cat_id=$row_cats['cat_id'];
$cat_title=$row_cats['cat_title'];
echo"<option value='$cat_id'>$cat_title</option>";
} ?></td></tr>
<tr><td><td><b>Product Brand</b></td><select name="product_brand"><option>Select Brand</option><?php
$get_brands="select * from brands";
$run_brands=mysqli_query($con,$get_brands);
while($row_brands=mysqli_fetch_array($run_brands)){
$brand_id=$row_brands['brand_id'];
$brand_title=$row_brands['brand_title'];
echo"<option value='$brand_id'>$brand_title</option>";
} ?>
</td></tr>
<tr><td><td align="right"><b>Product Image1</b></td><input type="file" name="product_img1"/></td></tr>
<tr><td><td align="right"><b>Product Image2</b></td><input type="file" name="product_img2"/></td></tr>
<tr><td><td align="right"><b>Product Image3</b></td><input type="file" name="product_img3"/></td></tr>
<tr><td><td align="right"><b>Product Description</b></td><textarea name="product_desc" cols="35" rows="10"/></textarea></td></tr>
<tr><td><td align="right"><b>Product Keywords</b></td><input type="text" name="product_keywords"size="50"/></td></tr>
<tr><td><td align="right"><b>Product Price</b></td><input type="text" name="product_price"/></td></tr>
<tr align="center"><td colspan="2"><input type="submit" name="submit" value="submit"/></td></tr>
</table>
</form>
</body>
</html>