You just need to fetch the content You can use cURL or file_get_contents()
cURL version:
<?php
$url = "https://www.tinkoff.ru/api/v1/currency_rates";
$curl = curl_init($url);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, TRUE);
$r = curl_exec($curl);
curl_close($curl);
$array = json_decode($r, true);
echo "<pre>";
print_r($array);
echo "</pre>";
?>
file_get_contents version:
<?php
$r = file_get_contents('https://www.tinkoff.ru/api/v1/currency_rates');
echo "<pre>";
echo print_r(json_decode($r, true));
echo "</pre>";
?>
Both of them will work unless the remote website requires you to be human (has extra verifications to stop robot requests). cURL would be a better way if that were the case because you can fake a user agent using a header array.
Once you have the array build it's just a matter of accessing the required data. using $r as an array result of the remote json structure.