I do actually have one right now, the problem is either the provider of the SSL or my domain (nameservers). Not really a web expert, so I don't know which would effect the website in regards to adding an SSL
Essentially, the setup of a SSL certificate works like this:
You purchase an SSL certificate, or use a free option such as LetsEncrypt or Cloudflare SSL. You'll usually have to complete a verification process when purchasing your certificate.
You install the SSL certificate to your web server.
You can then force https, for example with a .htaccess file in your XF main directory.
It seems like the easiest option for yourself here would be to simply use Cloudflare, which will automatically provide you with an SSL certificate. For full client-to-server encryption, you could use Cloudflare's provided SSL certificate .pem files etc...
This would involve registering your site over at https://cloudflare.com, and simply changing your nameservers over to the ones provided. It may take a while for your DNS changes to propagate, but once done you should be able to access your site at https://trade-mc.com/.