If you have a subdomain (something.ultifree.ml), then SSL isn't possible for your website, due to the way that SSL certificates are issued.
However, if you have your own domain, then the easiest way to get SSL would be through Cloudflare. You sign up on their website, then change your nameservers to theirs. The website will still be hosted for free by us, but you can then turn on SSL in the security settings of Cloudflare. You don't have to worry about renewing certificates or anything like that, they will handle it for you.
Using free SSL generators online will not allow HTTP verification to work due to our bot protection system, therefore you would have to use DNS verification using the DNS tools provided to you by the seller of your domain. I would recommend Cloudflare over manual SSL, simply because it is easier to manage.