You don't tell us the situation.
If you mean a clear space across the whole screen between one element like a table or div and another then the usual method is to add or increase the margin-top:-
<table style="margin-top: 30px;">................</table>
or same with a div, h1 heading, p tag etc;
If you mean a space within a div or table cell then use which is a text character but a blank one (a "hard" space rather than none at all so it comes with a standard width and height).