GIS and QGIS

A quick view on the menus in QGIS

The Main Menu and the indicated tools on the Toolbar are the two most frequently used means to trigger actions. Both menus are connected in a way, in many cases they give access to same actions. This can be clearly identified on the used icons in both. The icons in front of the "New...", "Open..." and "Save..." menu items in the [Project] menu are also used in the Standard toolbar  1 . By a "Right-mouse-click" on the Main menu or the Standard toolbar a "contextual" menu will pop-up which gives you the option to add tools to the toolbar. These are also accessible via the [View/Toolbars] menu.
The properties  2 , to be found in the [Project] menu too, gives access to settings on the main project level like: location of files; the Coordinate Reference System; Meta Data; and more...
Through the "Layout"  3  (a print-composer) it is possible to get a print of the map. In the "Layout" window, all elements (mapface, title, legend, scale, grid/graticule, marginal info, and more...) can be included, postioned and styled before either [Print] or [Save] as svg, pdf or image. When installing QGIS, as standerd set of tools and functionalities are loaded. The [Plugin]  4  menu gives access to a large number of additional tools for many different operations. These tools are developed by the community, and are free of use.
The [Vector] and [Raster]  5  6  menu gives quick access to a collection of operations.
The [Database] manager  7  allows users to interact with a database in a variety of ways.

The DB Manager Plugin is officially part of the QGIS core and is intended to be the main tool to integrate and manage spatial database formats supported by QGIS (PostGIS, SpatiaLite, Geopackage, Oracle Spatial, Virtual layers) in one user interface. The dbManager DB Manager Plugin provides several features. You can drag layers from the QGIS Browser into the DB Manager, and it will import your layer into your spatial database. You can drag and drop tables between spatial databases and they will get imported.
QGIS docs

To get access to the "Toolbox" or "Graphic Modeler", the [Processing]  8  menu has to be opened.
The [Help] menu  9  is an important entry for answers on how to use different elements in QGIS and can give direction in which tools are best to use.

Menus in QGIS

The menu bar provides access to various QGIS features using a standard hierarchical menu. The top-level menus and a summary of some of the menu options are listed below, together with the associated icons as they appear on the toolbar, and keyboard shortcuts. The shortcuts presented in this section are the defaults; however, keyboard shortcuts can also be configured manually...
...Although most menu options have a corresponding tool and vice-versa, the menus are not organized exactly like the toolbars. The toolbar containing the tool is listed after each menu option as a checkbox entry. Some menu options only appear if the corresponding plugin is loaded.

You'll work with different types of commands:

• Buttons execute a specific task when you click them.
• Tools are similar to buttons except they allow you to interact with the display before an action is performed. For example, the Zoom In tool allows you to drag a rectangle over a map to specify the new extent.
• A tool palette presents a collection of related tools.
• Combo boxes allow you to choose an option from a drop-down list.
• Text boxes or edit boxes allow you to type in text.
• Menus present a list of commands. A context menu is a floating menu that pops up at the location of the pointer when you right-click.