how to register a domain?

i wanna register a free domain on www.dot.tk but everytime i wanna copy-paste the jotform url to the coloum URL in there, it always say The URL you have given is not valid. why is that so? how to make my form url http://form.jotform.me/form/50498866093469 valid in dot.tk? so that i can register my own domain. 

The form's url is already a registered url so it's not possible for you to registered it. 

I will explain further. In order for you to have content online you need two things:

- The domain (i.e. www.mydomain.com),  which will give the url so people can access your content;

- Webhosting service, which will be a place where you will save/host your files.

For now you are just registering the url for your site which can be anything you choose (as long as it is available). It can be something like www.yourname.tk. 

After that you need a hosting service that can be connected to that url. There are some free hosting services that allow you to add your own domain. The hosting service you select will have instructions on how to add your domain to the webhost. 

Finally to have your form to show under your domain you need to embed the form using one the available methods. The iFrame method is the preferred method to embed:

If you need further support please let us know and we'll be glad to assist you.