How many employees can log in the account to create forms?

I have another question. If my company have an account with jotform how many employees can log in the account to create forms?

Please note that sub-user account feature is no longer available in free or other subscription plan. If you want to add sub-users, it is only available in enterprise plan: https://www.jotform.com/enterprise/

When my company will subscribe itself to a silver package for example so every user can use only one log in? By sub- user you mean each user can log in jotform from their individual account?

When my company will subscribe itself to a silver package for example so every user can use only one log in?

No it is no longer possible. You sign up for an account and upgrade to silver plan. Form needs to be created in your account and anyone with access to your account login credentials will be able to login and make changes. Other users will not be able to edit your form from their account. 

By sub- user you mean each user can log in jotform from their individual account?

Please note that sub-users will have their own Jotform account. You need to create forms in your paid account and then share forms with your sub-users. They will be able to access your forms from their own account. Please note this sub-user account feature is no longer available in free, bronze, silver or gold plans. It is only available in enterprise plan.

Can two people be logged in at the same time? Say my company has one general log in. If I am logged in and creating a form, can my colleague on his PC log in at the same time and create another form?

Yes, I believe that's possible.

Multiple logins are allowed. However, I would not recommend this if the multiple users will be working on the same form, because the changes made by one user can overrule the changes another user made. 

We have the Form Collaboration feature, that allows multiple team members to simultaneously create a form. Please check this guide: Understanding-Form-Collaboration.