When creating functions the parts inside brackets are called parameters. They are kinda like variables. The parameter for the function greeting is name. When you call a function you will put something inside the brackets, in this case you put in "Julia". This means that whenever you use the variable name inside that function it will be equal to julia. So if you did console.log(name) it would print Julia. If you changed what you put inside the brackets, so for example greeting('Jnagle') when it reaches console.log(name) it would print Jnagle.
But you want your function to say Great to see you Julia or Jnagle or whatever name you chose. So for that you can do
console.log("Great to see you,"+ name)
Remember a variable should not have quotation marks around it. So do not put +"name" and also the plus must be outside of the quotation marks. Your code would print "Great to see you, + Julia.".