In a thesis, report or book one can often find a list of figures and a list of tables. Latex provides a simple command for both of them which will collect all your figures and/or tables and automatically generate a list.
This is another great example which nicely shows how powerful LaTex is compared to some proprietary products available on the market. The two commands \listoffigures (lof) and \listoftables (lot) are used in the same way as \tableofcontents to generate lists with all your figures and tables.
The command \listoffigures will collect all the captions of your figures and include them in the list. Now it may happen that your captions are long which would results in an even longer list of figures, spanning over several pages. Therefore, the caption command provides the option to define a shorter entry displayed in the list of figures only whereas the text of the required argument will be displayed together with the figure. This applies for the list of table in the same way as it does for the list of figures.
\caption[short caption for lof/lot]{long figure/table caption}