Connecting Microtik 751

Hello everyone,
It is my first post here today. I would like to apologize if I am posting on the wrong place.
Comments and guidance will be very much appreciated.

I joined a company 6 months ago ad technical support and it is the first time that I came to know about Micro Tik.
We are using 751 2HnD to provide wifi to SOHO and 750 plus 2011 for bigger businesses.

Today I would like to understand about 751 2Hnd
The first port on 751 2HnD always take the cable / DSl from modem.
Then on ports 2,3,4 and 5 anything can be connected.
I have asked several questions to senior guys who are doing the day to day running of the business but did not get a correct answer to convince me .
My questions are as follows.

(1)What is Micro Tik 751 2HnD. A Modem or Router ? Because I have been told that when I call a customer just tell them to reset the white box which does not make sense to me but maybe to the customer.
When we use both 750 and 2011 we tell customerr to reset white square box and white rectangular box. I know thai ia a good guidance for the customer but the senior guys told me both are modems.
I want to know which is which?

(2)I would like to know where do we configure the splash page /captive page or landing page in SOHO with only Micro Tik 751 2HnD only in use?

(3)Where is the splash page configure when 751 and 2011 are in picture ?

I think this is all for now.
I have more questions but will ask as and when required.

Thanks a lot for replies and comments.

Scenemayer