Hi @JeannineBar ,
It's all about logic & built up a code accordingly as per requirement.
#ServiceNow use JavaScript you should know more about on it.
#For portal implementation, HTML, CSS, Angular script you should know.
#For UI page, Jelly script you should know.
For ServiceNow, you should know about client-side script, catalog client script, UI policy, Server-Side script like BR, Script include, Data policy, Schedule job, UI action client side as well as server side.
Few good sources please check out:
Learn MORE JavaScript on the ServiceNow Platform - ServiceNow Community
Scripting in ServiceNow Fundamentals On Demand - Now Learning
Please mark helpful & accept answer if it's really worthy for you.
