Hello. Welcome to ServiceNow World
Firstly start with Fundamental topics like Applications, tables, modules, form, list, fields, reports, notifications, acls etc then go with Scripting topics(before that you must know atleast basics of Javascript) Client side and server side
Then you can go to advanced topics such as update sets, integrations, etc
You can easily get full list of topics in google itself
You can refer these youtube channels :
SaaS with ServiceNow
Basico Servicenow
Tech with Pri
All of them explain concepts very well and provide practical examples. I studied from here during my initial training days
Hope it helps!
