Jamroom templates use Smarty 4. A template block wraps part of a template, from an opening tag to a closing tag, and decides whether or how often that part is shown. Template functions, such as {jrCore_list}, are a single tag instead.
{if jrUser_is_logged_in()}
<a href="{$jamroom_url}/user/logout">Log out</a>
{/if}The part between {if ...} and {/if} is shown only when the condition is true. Add {else} for the other case, and put ! before a condition for "not".
These Jamroom functions are made for {if}:
You can also test any template variable, such as {if $profile_quota_id == 2}. {debug} shows the variables a template has.
The Smarty documentation explains every block and operator.