How do you get the free version of Microsoft Azure?

Hi,

We have a customer we are migrating to 365 from an on premise AD server. We have completed this using the active directory sync tool and Azure. We just downloaded the free trial of Azure as on the website it says there is a free version and that's fine for what we want it to do. We are now getting emails saying that our subscription is going to expire. The way I'm assuming Azure works is you can only download the trail and it gives you all the features and then if you don't sign up for a paid for package it will just disable all the paid for features and you can only use the free stuff?

My question is, is this correct? I don't wan't all the users in a few days to not be able to reset passwords or access emails or anything like that. So just wanted to clarify if I need to select what type of subscription I want to use?

Regards,

James