How can the subusers login?

UPDATE: Effective October 2018 the Sub-User feature has been discontinued and is no longer available for creating new sub-users. If you had been using this feature previously, you're grandfathered. 

 If you would like to have additional users added to your account, please check out JotForm Enterprise.

When you Share Forms with a Sub-Account User, that means you are sharing the form to another independent JotForm Account. So this user needs to login to www.jotform.com, with his already registered account username and password.

Then, we he logged in, he will be able to see the forms shared to him like this:

Let us know if you have more questions, we will be glad to assist you.