The \vspace command adds vertical space. The length of the space can be expressed in any terms that LaTeX understands, i.e., points, inches, etc. You can add negative as well as positive space with an \vspace command.
If \vspace appears in the middle of a paragraph the space is added after the line containing it.
LaTeX removes vertical space that comes at the end of a page. If you don't want LaTeX to remove this space, include the optional * argument. Then the space is never removed.