Making paragraphs
A paragraph is ended by one or more completely blank lines—lines not containing even a %. A blank line should not appear where a new paragraph cannot be started, such as in math mode or in the argument of a sectioning command.

\indent
\indent produces a horizontal space whose width equals to the \parindent length, the normal paragraph indentation. It is used to add paragraph indentation where it would otherwise be suppressed.
The default value for \parindent is 1em in two-column mode, otherwise 15pt for 10pt documents, 17pt for 11pt, and 1.5em for 12pt.

\noindent
When used at the beginning of the paragraph, this command suppresses any paragraph indentation, as in this example.

.. end of the prior paragraph.

\noindent This paragraph is not indented.

It has no effect when used in the middle of a paragraph.
To eliminate paragraph indentation in an entire document, put \setlength{\parindent}{0pt} in the preamble.

\parskip
\parskip is a rubber length defining extra vertical space added before each paragraph. The default is 0pt plus1pt.

Marginal notes
Synopsis:

\marginpar[left]{right}

The \marginpar command creates a note in the margin. The first line of the note will have the same baseline as the line in the text where the \marginpar occurs.
When you only specify the mandatory argument right, the text will be placed
in the right margin for one-sided layout (option oneside, see Document class options);
in the outside margin for two-sided layout (option twoside, see Document class options);
in the nearest margin for two-column layout (option twocolumn, see Document class options).
The command \reversemarginpar places subsequent marginal notes in the opposite (inside) margin. \normalmarginpar places them in the default position.
When you specify both arguments, left is used for the left margin, and right is used for the right margin.
The first word will normally not be hyphenated; you can enable hyphenation there by beginning the node with \hspace{0pt}.
These parameters affect the formatting of the note:
\marginparpush 	Minimum vertical space between notes; default ‘7pt’ for ‘12pt’ documents, ‘5pt’ else.
\marginparsep 	Horizontal space between the main text and the note; default ‘11pt’ for ‘10pt’ documents, ‘10pt’ else.
\marginparwidth 	Width of the note itself; default for a one-sided ‘10pt’ document is ‘90pt’, ‘83pt’ for ‘11pt’, and ‘68pt’ for ‘12pt’; ‘17pt’ more in each case for a two-sided document. In two column mode, the default is ‘48pt’.
The standard LaTeX routine for marginal notes does not prevent notes from falling off the bottom of the page.