I'm Learning and need to understand how costing is works

Hi All , 

I started recently to learn Azure and my goal is to complete Azure Administrator exam AZ-103

Unfortunately i don't have any way to practice Azure at work so i found the Hands On labs by Microsoft but I think i still need to create an account that will be free for 1 month and have some credit. 

I think I'll need to practice for than 1 month but worried about the cost , say i don't add any resources to the subscription that I'll create ... will i pay any money at the end of the month ?

I want to learn Azure , to browse and create VMs and delete them immediately , create small storage and delete them immediately . Do you think there is any way to avoid the cost ?

My sceond question is about the hands on labs , they say 40 min per lab ... does it mean if i used it for 40 Min and wanted to use the same Lab again it will not work ? Is it one time use ?

Thanks 

Immer