Wit your Formula
=TEXT(Created, "dd mm yy")
You provide 2 parameters to the TEXT( ) function,
telling it to format (replace with values) Created with the format: "dd mm yy"
The output is: day month year
"11 12 16"
The TEXT() function was modeled after (but is not the same), the Excel TEXT () Function,
fairly good documented in the Text Function Examples Excel Sheet
So characters in the format string have special meaning
I don't know Why b is converted, but with
=TEXT(Today()-365, "b")
=TEXT(Today(), "b")
=TEXT(Today()+365, "b")
it is fair to say it is the two digit Year
Interesting to note is that y is the same as yy
And the SharePoint TEXT() function does not care about upper/LOWER case
To exclude characters from being formatted you have to escape them with a slash: \
=TEXT( Today() ,"dd mm yyyy \# DDD DD MMMM YYYY")
&"<br>"
&TEXT(TODAY(),"\b:b \d:d \h:h \m:m \s:s \y:y")
&TEXT(TODAY(),"\<\B\R>\B:B \D:D \H:H \M:M \S:S \Y:Y")
Outputs:

b - year (but why?)
d - day
y - year
h- hours = 0 because Today() has no timestamp
m - minutes
s- seconds
To make the <BR> work as a Line Break you have to output the Text as HTML by setting its field output to anything BUT Text (it is a trick)
Number will align the text to the right (because it is supposed to be a Number),
Set it to DateTime to have the text Left Aligned
Note, I used Today() as an example, be aware it does NOT recalculate every day like it does in Excel: The Formula is only updated when the Item changes, so Today() is effectively the same as Modified (without the time stamp!)
See https://sharepoint.stackexchange.com/questions/151144/how-to-use-today-and-me-in-calculated-column/151336?s=1|0.0000#151336
Most basic Excel functions are the same in SharePoint,
see:
https://www.365csi.nl/vm365com/365coach/#/Calculated_Column_Functions_List
=TEXT(Created,"dd <\br/> mm <\br/> yy"). If you want to render theas text you have to set it to Single Line of Text, as anything else will make the Browser interpret it as HTML – Danny '365CSI' Engelman Dec 11 '16 at 13:40