静态调用非静态方法PHP [重复]

I am new to PHP, and have encountered many problems with some code that I am writing that I have been able to solve. But, one problem seems to never disappear. I constantly receive the error message Fatal error: Non-static method mysqli::select_db() cannot be called statically. The code the error refers to will be below. If anyone has a solution to this problem, as well as an explanation, that would be most helpful.

$db_selected = mysqli::select_db($link, DB_NAME);

if (!$db_selected) {
    die('Can\'t use ' . DB_NAME . ': ' . mysql_error());
}

EDIT

Other Stack Exchange questions are not helpful for this situation. Explaining to me the fact my question is low-level does not help, as I already understand that and acknowledged it above.

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$db_selected = mysqli_select_db($link, DB_NAME);

if (!$db_selected) {
    die('Can\'t use ' . DB_NAME . ': ' . mysql_error());
}

You're trying to call a function that's not avaiable, you have to choose a DB like above.

Edit:
But i recommend just selected the DB when you're instantiating the connection like this:

$mysqli = mysqli_connect('HOST', 'USEER', 'PASS', 'DB');