How do would I create a cloud varible (High score) for a game

<script>
// I want to create a cloud variable (high score)
// But I don't know how. 
var click = 0;
document.getElementById("High_score").innerHTML = cloud_varible;
function btn(){
click ++;
document.getElementById("p").innerHTML = click;
}
if (clicks < cloud_varible){
clicks = cloud_varible
document.getElementById("High_score").innerHTML = cloud_varible;
}
</script>
<button id="btn" onclick="btn();">click</button>
<p id="p">clicks: </p>
<p id="High_score"></p>

I've looked at various wbsite but none seem to awnser my qestion. I have intermediate-basic knoledge in javascript. Intermediate-Advance HTML and intermediate Knoledge in CSS and basic knowledge in PHP.

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