Here we are discussing how to create and call custom popup using Magento 2’s Popup Modal Library.

You should create a module first, then after create a requirejs-config.js file at app/code/CustomVendor/CustomModule/view/frontend/

var config = {
    paths: {            
         'myjs': "CustomVendor_CustomModule/js/customfile"
      },   
    shim: {
    'myjs': {
        deps: ['jquery']
    }
  }
}

You need to create customfile.js at app/code/CustomVendor/CustomModule/view/frontend/web/js/

<script>
    require(
        [
            'jquery',
            'Magento_Ui/js/modal/modal'
        ],
        function(
            $,
            modal
        ) {
            var options = {
                type: 'popup',
                responsive: true,
                innerScroll: true,
                buttons: [{
                    text: $.mage.__('Continue'),
                    class: 'mymodal1',
                    click: function () {
                        this.closeModal();
                    }
                }]
            };

            var popup = modal(options, $('#custompopup'));
            $("#click-here").on('click',function(){
                $("#custompopup").modal("openModal");
            });
        }
    );
</script>

Add following code in your phtml file:

<div data-mage-init='{"myjs": {}}'>
    <a href="#" id="click-here">Click Here</a>
</div>


<div id="custompopup" >
    This is custom popup using magento popup modal.
</div>