Assign sets a variable in your template.

{% assign foo = 'monkey' %}

You can then use the variable later in the page.

{{ foo }}

Note that we advise you to prefix your variables to avoid problems with some generic names (i.e. url, link, flash to name a few) that may be used in Edicy in the future. If your site name is "BeeGees" then naming your variables in style beegees_link will ensure that we at Edicy do not come up with such variable names.