"fill in" versus "fill out"

[Attila]

I was taught that a person fill in a request and people who're saying fill out are wrong.

But today I found in a dictionary that both of the expressions can be used.
In the future, should I say I fill in the request form or I fill out the request form ?

And a second question regarding this:
Supposing there's a request form and I explain someone how to fill in/out the first 3 question. Then I tell the person that he should fill in/out the rest of the questions as appropriate. (because the rest is very simple to understand)

fill in/out as appropriate - is it correct?

[Mister Micawber]

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Both are fine in all instances, Hun.
.
_________________
Native English teacher at Mister Micawber's

[Attila]

[Mister Micawber]

.
Attila the Hun was a famous king, as I hope you know. Hun is also word play with hon, which is short for 'honey', a term of endearment commonly used in casual speech.
.
_________________
Native English teacher at Mister Micawber's

[Attila]

I would have never thought that a non European knows where this name come from or even knows the king with that name.

I guess you exposed me as an Hungarian.

Now I might as well change the location name from Europe to Hungary in my profile.

[Tamara]

Hi

[Yankee]

Hi Tamara

You're right about that.

But there is still one very small, but critical difference between "hon" and "Hon." (besides the fact that "Hon." isn't a spoken form).

Hi Attila

Atilla the Hun is a name that is quite well-known ... even outside Europe. If you went to the USA and told people your name is Attila, it wouldn't surprise me to find out that you'd instantly been given the nickname "The Hun". So, in that regard, Mr. Mic has been quite delinquent in his issuing of nicknames. But you have to admit, the "hon pun" was good.

Amy

[Tamara]

[Jamie (K)]