Hi 
The proper guides/manuals/books are here;
https://wiki.documentfoundation.org/Documentation/Publications
(they are available elsewhere too but that wiki-page is the most up-to-date
and even has chapters before the full book has been completed for
publication). The proper guides are great at giving a strong overview to
help anticipate how everything works.
If you scroll further down that page (or click on the table-of-contents)
then you get to some quick-reference cards
https://wiki.documentfoundation.org/Documentation/Publications#Desktop_Reference_Cards
these can be useful to have printed out but they might be a little
out-of-date now and thus miss a lot of new features, or screen-shots might
look a bit archaic or show things looking rough that are really smoooth
now. Even so they are excellent for "at a glance" help. Handy to have on
a wall easy to read from a desk or few.
There is an FAQ (=frequently asked question) at
https://wiki.documentfoundation.org/Faq
to dip into to look-up things quickly.
The in-built help is useful. In the top icon-bar just click on the little
blue question mark. Sometimes the English one is a bit geeky or might be
misleading or inaccurate in places because Office (i mean LibreOffice but i
often just use Office for short because i use it so much) develops so fast
that it's not possible to keep up all the time. Not that things keep
changing around just that Murphy's Law suggests that the 1 thing you need
to look-up turns out ot be a new feature. It's usually pretty good for
quickly looking things up.
There are a few videos and other things listed here;
https://wiki.documentfoundation.org/Documentation/Other_Documentation_and_Resources
Buried somewhere in there is an excellent book on how to program macros to
do some really useful stuff. Also here;
https://wiki.documentfoundation.org/Macros
Often people use Extensions/Add-ons
http://extensions.libreoffice.org/
but being able to program in your own stuff can be quite rewarding.
There is an online training resource at;
http://www.spoken-tutorial.org/
for example on Writer, in English;
http://www.spoken-tutorial.org/tutorial-search/?foss=LibreOffice+Suite+Writer&language=English
There is a comparison betweeen LIbreOffice and MS Office
https://wiki.documentfoundation.org/Feature_Comparison:LibreOffice-_Microsoft_Office
but again it's already out-of-date, or maybe perpetually out-of-date due to
the rapid development of LibreOffice. Mostly you'll notice that
LibreOffice really is cross-platform and even on platforms or niche markets
where LibreOfrfice itself doesn't have a presence there is inevitable
something else in the same eco-system that does work well with LibreOffice
files
Of course MS Office seems to try hard to be incompatible with everything
else because that way people are kinda forced into buying MS Office.
However, most of the problems you find are also problems if files are
opened with a different version of MS Office than the version the file was
created with. For example a table created in MS Office 2007 might well not
work in MS Office 2010 or 2013. Files created in anything other than MS
Office almost never have a problem when opened in LibreOffice regardless of
version.
Hopefully some of these links prove useful and most will point to other
links and to other resources.
Regards from
Tom 