"Do you mean for tables tags?"
"Perhaps you mean <TD> tags?"
That as well. Set the table width at, say 95%. Inside the table, set the td width at a % as well. The point being is that the table will expand to the ratio of the viewing area, and not be fixed. Make an HTML page and then shrink/expand your browser viewing area to see how it works.
"OK, but how then do you control the width of columns and exact layout of images etc?"
It won't look exactly the same for every computer, that's the point. If you want it exact use exact measurements.