How to Change Rails Env on Unicorn?

Hello i’m new to ruby application deplloy, but when i using to learn. but when i learn rails i used Webrick locally and i could setup and use many Envs, how i do that in unicorn? how can i have online application running in a version when i chage, upgrade and test my application without interfer in my running application?

PS: How i see the realtime log in unicorn, like the webrick when i run the “Rails s”?