I took a bit of your script and this is how you can make it. Hopefully I'm good enough to explain so you understand how to use it.
<?xml version="1.0" encoding="utf-8" ?>
<j:jelly trim="false" xmlns:j="jelly:core" xmlns:g="glide" xmlns:j2="null" xmlns:g2="null">
<g:evaluate var="jvar_gr" object="true">
var gr = new GlideRecord("sys_user");
gr.addQuery('sys_id',gs.getUserID());
gr.query();
gr;
</g:evaluate>
<j:while test="${jvar_gr.next()}">
dear ${jvar_gr.getValue('email')}
</j:while>
</j:jelly>
I learned my first jelly things while looking at the TechNows jelly episodes. You can find the first one here: TechNow Episode 1 | ServiceNow Jelly Scripting Part 1 of 3 - YouTube
If you want to use jelly variables you need 2 things.
1. Put jelly="true" in the evaluate like this:
<g:evaluate jelly="true">
2. when you refer to a jelly variable in the evaluate you need to put jelly. before the variable name like this:
var users_email = jelly.jvar_this_is_the_jelly_variablename
if you got any other questions, feel free to ask
//Göran
