CMS Made Simple Forums

I have a site on Joomla. Now I'm transferring this site on CMS MadeSimple. I have questions:
1. How to transfer users from Joomla to CMS MadeSimple?
2. What kind of a module is better to use in authorizing user in the front-end?

If you know MySql, you can look at the Joomla users table and the CMSMS users table, and convert the data into the CMSMS format.

Yes, I know, but, as I know, passwords are encoded in Joomla. How to decode them into CMS MadeSimple?

I think both use md5 encoded passwords, so this should work without any conversion.

But notice that users in Joomla != users in CMSms.
In CMSms backend and frontend users are managed separately.
So if you import your users from Joomla to CMSms make sure you import those users with backend access into the cms users table and those with frontend only access into the FrontEndUsers module.