Setup contains administrative definitions. Object Manager groups the fields, record types, layouts, and rules for one object. Quick Find narrows the Setup tree; it doesn't search customer records or apply a list filter. Start by checking whether your task changes configuration or changes a record.
The same label can appear in more than one place. A case record belongs in the Cases list, while its field definition belongs in Object Manager. Keep that distinction when you move between screens. This independent practice org uses original controls and fictional records, but the destinations and vocabulary follow Salesforce administration. Nothing you save here changes a real Salesforce org.