Well the first thing to do is to see if your webhost has GD enabled, run this code
<?php
echo '<pre>';
var_dump(gd_info());
echo '</pre>';
?>
and if you have GD support then you will get a page display like this
array(12) {
["GD Version"]=>
string(27) "bundled (2.0.28 compatible)"
["FreeType Support"]=>
bool(true)
["FreeType Linkage"]=>
string(13) "with freetype"
["T1Lib Support"]=>
bool(true)
["GIF Read Support"]=>
bool(true)
["GIF Create Support"]=>
bool(true)
["JPG Support"]=>
bool(true)
["PNG Support"]=>
bool(true)
["WBMP Support"]=>
bool(true)
["XPM Support"]=>
bool(false)
["XBM Support"]=>
bool(true)
["JIS-mapped Japanese Font Support"]=>
bool(false)
}
After that Google for GD tutorials there's loads our there.