There are a few options to make a field required on an object. Unless you are creating a brand new object, option 1 is usually the best choice.
Option 1: Make the Field Required on the Page Layout
This option works well for objects with existing data and/or automation. See this related article for instructions on how to make a field required on a page layout.
Option 2: Make the Field Required at the Field Level
This option works well when creating fields for a new custom object. To do this select the 'Required' checkbox when creating or editing the field in setup.
Option 3: Make the field Required Only When Certain Criteria are Met Using Validation Rules
This option can be used for situations where a field is only required if other fields have a certain value. For example, a validation rule could be configured to require a value in the 'Other Language' text field of Contact records when a value of 'Other' is selected in the 'Language' picklist field.