https://developer.servicenow.com/dev.do#!/learn/courses/sandiego/app_store_learnv2_learnmore_sandiego_learn_more/app_store_learnv2_learnmore_sandiego_form_and_list_layouts/app_store_learnv2_learnmore_sandiego_what_is_form_designer The Form Designer is a tool that allows you to create and customize forms on the ServiceNow platform. The Form Designer has four main components:
Form layout: The form layout shows the preview of the form and allows you to drag and drop fields, sections, and related lists onto the form. You can also resize, reorder, and delete the elements on the form layout.
Page header: The page header shows the name of the table and the form that you are editing. You can also access the form properties, save the form, and switch to the form view from the page header.
Field navigator: The field navigator shows the list of available fields for the table and allows you to search, filter, and add fields to the form. You can also create new fields and edit existing fields from the field navigator.
Schema map: The schema map is not part of the Form Designer. The schema map is a separate tool that shows the relationships between tables and fields on the platform. You can access the schema map from the System Definition > Tables module or from the context menu of a table.
References:
[Form Designer]
[Schema map]

https://docs.servicenow.com/bundle/tokyo-application-development/page/app-store/dev_portal/API_reference/GlideQuery/concept/GlideQueryGlobalAPI.html#GlideQueryAPI
https://docs.servicenow.com/bundle/tokyo-application-development/page/app-store/dev_portal/API_reference/glideRecordScoped/concept/c_GlideRecordScopedAPI.html

A possible reason to build a custom app is to fulfill a specific use case on internal processes. For example, you may want to digitize a manual process that is not covered by an existing ServiceNow solution, such as managing inventory, tracking expenses, or scheduling events. Building a custom app on the Now Platform can help you automate workflows, improve data quality, and provide better user experiences. The other options are not valid reasons to build a custom app. To avoid using a code repository like GitHub or GitLab is not a reason to build a custom app, as you can still use source control integration with your custom app development. To create a custom integration for a 3rd party system is not a reason to build a custom app, as you can use integration tools such as IntegrationHub or REST APIs to connect with external systems without creating an app. To replace ServiceNow base tables is not a reason to build a custom app, as it is not recommended to modify or delete base tables that are essential for ServiceNow functionality. Reference: Build Custom Apps in ServiceNow - eBook

https://developer.servicenow.com/dev.do#!/learn/learning-plans/quebec/servicenow_administrator/app_store_learnv2_automatingapps_quebec_scheduled_script_execution_scripts The objects that you can use in a Scheduled Script Execution (Scheduled Job) script are GlideSystem and GlideRecord. GlideSystem provides methods for performing system operations, such as logging, running background scripts, or getting system information. GlideRecord provides methods for working with records in the database, such as querying, updating, inserting, or deleting records. The current object is not available in Scheduled Script Execution scripts, as it refers to the current record on a form or list. The GlideUser object is also not available, as it refers to the current user session. Reference: Scheduled Script Execution, GlideSystem, GlideRecord

Application Files are ServiceNow artifacts comprising an application. An application is a group of files and data that work together to provide a service or functionality. An application file is a specific type of file that belongs to an application, such as a table, a script, a form, a business rule, a UI action, etc. Application files define the structure, logic, and interface of the application. An XML export of an application's table records, XML exports of an application's Update Set, and CSV files containing data imported into an application are not examples of application files, as they are data formats that can be used to transfer or store information related to an application, but not the application itself. Reference: Application Files