How do I get key data from JSON?

Hello.

Never used JSON untill not because i have to :)

Can someone tell me how do i get a string value from a key ?

Right now i have something like this

Event -> Set testid to Plugin.curReceipt

and as i see in testid i have a JSON string after the action is made its something like this {"orderid":"the-id-i-want-to-extract".......

Can someone tell me please how do i extract the order id and set it in a global variable or so...

Newbie here:)

Thank you in advance