Hi 
Chapter 3 of the "Getting Started Guide", the chapter about "Styles and
Templates". In MS Office their equivalent can often cause problems but in
LibreOffice the system is different and makes it MUCH easier to produce
much higher quality documents with much less effort.
https://wiki.documentfoundation.org/Documentation/Publications
At the moment it sounds like you are formatting directly inside the content
of the document. For the most part, most of the document probably could do
with looking consistent and many of your headings and so on also being
consistent with each other. Future documents may well need to have the
same levels of consistency. At the moment you are maybe trying to remember
adn struggle a bit to try to force it all to behave.
Using styles, even a tiny bit, can drastically reduce the amount of direct
formatting you need to do and that can save quite a bit of time. Each time
you have to reach for the mouse to apply formatting it reduces your
productivity. Being able to keep yoru hands on the keyboard and use simple
keyboard combinations such as;
Ctrl B to switch "bold" on/off and
Ctrl I to switch "Italics" on/off and
Ctrl U to switch "Underline" on/off
along with
Ctrl x to cut (x looks a little like a pair of scissors)
Ctrl c to copy
Ctrl v to paste (v looks a bit like a downwards arrow)
and of course
Ctrl left/right arrows to skip a word at a time
All combine to make your typing much faster and with less need to break
your concentration. Touch-typing courses often suggest that it's better to
leave all the formatting until after a significant amount of a document has
been typed. This can work quite well wrt headings but it helps to be able
to apply emphasis without hunting for the mouse and then repositioning your
fingers again afterwards.
To open Styles just press F11, Then look up beside where you would normal
set your font to see the name of the style you are using in the body of the
contents: hopefully either "Text body" or "Default" and right-click on the
appropriate one in the styles pop-up dialogue-box to modify it.
I hope this helps!
Regards from
Tom 