This is how the custom Modal plugin tags syntax works:

You place a starting {modal} tag and a closing {/modal} tag in your content (in an article, module, anywhere you want).

The modal tag supports several attributes and modal types, which we'll see below. Between these plugin tags you can place anything you want to use as a link to open the modal popup.

{modal url="sample-articles/my-article"}Click here!{/modal}

The clickable link can be text, or a custom image, or basically anything you want. Anything you place between the modal tags will be used as link to open the modal.

For example, to open a modal via a custom image, simply have the {modal} tags surround your desired image:

{modal url="sample-articles/my-article"}{/modal}

Modals also comes with a handy editor button to help you insert the code you need.