components and variables - inspector problems

very simple question (hopefully) with s simple answer. I got a script from one of my friends and it used public variables to get the components<, in unity 5 how do I declare what component it should be associated with?

(I tried the little circle thing and nothing came up)

after the monobehavior line you do :

public typeofvariable nameofvariable
example:
public Rigidbody myrigid ;

in start you assign :
nameofvariable = getcomponent();
example:
myrigid = getcomponent();

in other functions such as update , you can access through :
nameofvariable.anyfunction(etc)
example:
myrigid.velocity() etc…

Hope it helps