JavaScript Programming in Dynamics 365

Hi Seniors, 

Folks, I am new to JavaScript programming, but functional certified in D365 CRM, now wants to make bit of programming skills as well: I need help to code following scenario:

I have two entities :

Entity A -> Attributes -> CalibrationID (Number), Name (Single Line Text), Calibration Min (Float Number),  Calibration Max (Float Number)

Entity B -> Attributes -> ID (Number), Machine Name (Single Line Text), CalibrationID

Entities have One(Entity A) to Many(Entity B) relationship.

Now on form of entity B, I want when user selects from CalibrationID lookup(which showing Calibration Name actually), system shows Calibration Min and Max value which are actually fetched from Entity B according to selection 

(I know its very common task for seniors but for me its Sky Scrapper ;) If somebody can suggest code with help to understand it will be a great help.

I have one more question as well, Is trial D365 online instance pre-configured for programming, I mean when somebody use xrm.page etc etc in javaScript code does xrm(SDK) is referenced somewhere already (which we used to do manually in c# programming by the use of 'using' keyword , if not how we can do it??

Any help, will be a great help :)

Cheers