[ksa]

WinterGuder, а так?

<div class="plus">
    <label for="">Input First Number :</label>
    <input type="text" id="value1">
    <p>+</p>
    <label for="">Input Second Number :</label>
    <input type="text" id="value2">
    <br><br><br><br>

    <button onclick="plus()">Ok</button>
</div>
<script>
function plus() {
    let v1 = Number(document.getElementById('value1').value);
    let v2 = Number(document.getElementById('value2').value);
    let result = v1 + v2;
    alert(result)
}
</script>