Figures and tables have outer structures, <figure> and <table> which can contain a <title> (for cross-references, such as in a list of figures) and a <caption>. The presence of a <caption> generates a number for the figure or table. These outer structures also generate some vertical separation between surrounding elements.
A <table> may only contain a <tabular>, which is the structure containing the rows and columns of a table. Details can be found in Section 6.11.
A <figure> is more liberal than a <table> and may contain a variety of items. Most probably, you will include an <image> (see Section 3.6).