Redirects in Prestashop 1.7

Redirects to Frontend

Tools::redirect('index.php');
Tools::redirectLink('index.php');
$this->canonicalRedirection('??');

Redirects to Backend

Tools::redirectAdmin('urlHere');
Tools::redirectAdmin($this->context->link->getAdminLink('AdminControllerHere'));
Tools::redirectAdmin(Context::getContext()->link->getAdminLink(AdminDashboard::class));

How to generate an URL

See this article on how to generate an URL in Prestashop