Main functionality + some styling.

index.php

 <?php
 $hash = null;
 if(isset($_POST)) {
-	// Do hash
+	$input = $_POST['input'];
+	$type = strtolower($_POST['type']);
+
+	if($type == "sha1") {
+	    $hash = sha1($input);
+    } else if($type == "sha256") {
+	    $hash = hash('sha256', $input);
+    } else if($type == "md5") {
+	    $hash = md5($input);
+    } else {
+	    $hash = "Not-supported hashing method selected";
+    }
 }
 ?>
 
@@ -24,10 +35,17 @@ if(isset($_POST)) {
 		<h1>Hash Online</h1>
 		<h5 class="text-muted">Hash SHA1, SHA256, MD5 and more online</h5>
 
-		<form action="/" >
+		<form method="post" action="/" class="mt-5">
 
 			<input type="text" class="form-control" name="input" id="input" placeholder="Your input">
 
+            <label for="type">Hashing method</label>
+            <select class="form-control" name="type" id="type">
+                <option value="SHA1">SHA1</option>
+                <option value="SHA256">SHA256</option>
+                <option value="MD5">MD5</option>
+            </select>
+
 		</form>
 
 		<?php