<?phpThe only thing that you should take care of is that NOTHING should be printed before the header() function call.
echo "I don know what to do next";
Now if you need to call this header function in the middle of any of your html design- what to do ? Simple call ob_start() at the very first line of your page then call have all your html tags,call your header() function and and call ob_end_flush() immidiately after header() function call. The code should look like as follows :
//Your html and or other code to print html
echo "A line before header() call";