Explanation
Collections are temporary tables that store session-specific data in memory. They can be used for various purposes in APEX applications. Some uses of collections are:
You insert, update, and delete collection information using PL/SQL API APEX_COLLECTION. This API provides several procedures and functions to manipulate collections and their members.
Use collections to temporarily capture one or more nonscalar values. For example, you can use collections to store the results of a query, the values of page items, or the selections of a report.
Collections can be accessed, manipulated, or processed during a user's specific session. For example, you can use collections to pass data between pages, perform calculations on collection members, or create reports based on collections.
Collections do not enable you to store rows and columns in the current session into database tables.
Collections are stored in memory and are not persistent across sessions.

Explanation
An interactive grid is a customizable report that allows end users to modify the data and layout of the report.
End users can change the report layout by using the Actions menu or by dragging and dropping columns. They can also create private reports that save their personal preferences for the report. These features are available for both editable and noneditable interactive grids. Verified References: Using an Interactive Grid - Oracle Help Center, Example Interactive Grid - Oracle Help Center

Explanation
The Create Application Wizard is a tool that allows developers to create a new application by following a series of steps. Some of the actions that you can perform using the Create Application Wizard are:
Reorder application pages. You can use the Reorder Pages option in the Pages step to change the order of the pages in your application by dragging and dropping them.
Add or delete application pages. You can use the Add Page or Delete Page options in the Pages step to add new pages or delete existing pages from your application. You can also use the Create Page Wizard to create additional pages after creating the application. You cannot upload JavaScript or CSS files required for an application or change the application authorization using the Create Application Wizard.
You can use other features in App Builder to perform these actions, such as Shared Components > User Interface > Files and Shared Components > Security > Authentication Schemes. Verified References:
[Creating an Application Using the Create Application Wizard - Oracle Help Center], [Create Application Wizard - Oracle APEX]

Explanation
Open Door Credentials is an authentication scheme that allows anyone to access your application using a built-in login page that captures a user name. You can use this scheme for testing purposes or for applications that do not require secure authentication. You can select this scheme from the Authentication Type list when creating or editing an authentication scheme. References: [Understanding Authentication] and [Creating an Authentication Scheme]