They are not really secrets but unless you have been shown them, then you won’t know about them. And as I write this, I am aware that I too made these mistakes when I first started using computers.
First may I say that I think Microsoft Word is a fantastic tool as it allows people with almost no training in computers, write letters and CV’s and all sorts of simple documents. It may be responsible for the crime that is “the (mis)use of Comic Sans” but it does get the job done, most of the time. The problem is that when the documents get a little bigger or complex, the wheels start to come off the cart.
Because small documents can be literally hacked together, there is no need for consistency in a one page document as long as it looks OK when printed. However when the page count gets bigger and the number of sections increased, the style of the document begins to change throughout the document. This is because as we create a document we need to make little decisions about hoe it will look as we go. This problem is doubled if there is any collaboration in a document. Both contributors will make their own decisions as they go and usually they will be different. For example, at the end of each sentence some people mistakenly put two spaces after the full stop, thinking it’s the right thing to do. (Double spaces are a throwback to the days of mono-spaced typewriters where it was not easy to see the end of a sentence however these died out years ago with proportional fonts and so too should the practice of double spaces.)
There is a simple button which reveals (mostly) what is going on in a word document and it looks like this 
You’ll find it in the centre if the menu bar and it is used to show the hidden characters.
To activate it, just press the button and to turn it off, press it again.
The first thing you will see is that the page will probably look much more cluttered and if the document has been written by somebody else, you may get an insight into a colleague you weren’t expecting. I have seen words on the right hand side of the page, put there by typing spaces across the page as opposed to right aligning the text. A really common one is starting a new page by pressing the enter key a number of times until a new page appears as opposed to putting in a page break.
So what will you see and what are they?
The first thing you should see is our little friend on the button .
This is what you get when you press the enter key. It marks the end of a paragraph. That is important about that is that often there is extra space added below a paragraph which separates it from other paragraphs. Some like to put an extra space between paragraphs to give them definition and knowing no better put in an extra carriage return. Actually a carriage return (Typewriter speak) is achieved by pressing SHIFT and ENTER at the same time. A page break is achieved by pressing CTRL and ENTER at the same time. Really what they should do is to change the space between the paragraphs in the style definition.
The other common ones are :
The first is a space and it is between every word. The arrow is a tab mark and the third is the carriage return I just mentioned. This just skips to the next line with without any extra space.