if you click on an event, in the code window, top right - click on the “?” It tells you, depending on the event, when various things are accessible.
E.g
onApplicationInit
This event occurred before the application execute the SQL, and execute only once.
Is used to do verifications of variables, and security verifications.
Ex:
if ([glo_var_department] != ‘financial’){
sc_redir(app_x.php);
}
onScriptInit
These formulas are executed before the application starts. At this moment, the application locals variables are not available.
onLoad
This event its executed before the form is loaded. In this moment all the applications variables are availables.
On your other point, variables like {lang_sec_app_description} are replaced with values as defined in “Locales | Application Language”. You can either delete that “{lang_sec_app_description}” entry from the field and replace it with direct text of your own. Or you can go to Locales | Application Language, and define what value {lang_sec_app_description} has. Use the search at the bottom left to find that variable and update it as you see fit.