Example showing various styles of relative positioning with TikZ.

inlineNode.tex

\documentclass{minimal}

\usepackage{tikz}

\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{5pt}

\begin{document}

\begin{tikzpicture}
  \draw[->] (0,0) -- (5,0) node[above]{Hello, world!};
\end{tikzpicture}

\end{document}

namedCoord.tex

\documentclass{minimal}

\usepackage{tikz}
\usetikzlibrary{positioning}

\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{5pt}

\begin{document}

\begin{tikzpicture}[
  Name/.style = {font={\bfseries}}
]
  
  \coordinate (A) at (0,0);
  %            ^---- A name for the node/coordinate
  \coordinate (B) at (5,1);
  \coordinate (C) at (3,4);
  
  \draw (A) -- (B) -- (C)  -- cycle;
  
  \node (A-label) [left=1ex of A, Name] {A};
  \node (B-label) [right=1ex of B, Name] {B};
  \node (C-label) [above=1ex of C, Name] {C};
  
  \node [above left = 2 em of C] {This is a relatively positioned node!}
    edge[out=270,in=180,thick,->] (C-label);
  
\end{tikzpicture}

\end{document}