For reference, the names and functions of the keys of your computer's keyboard.
Top Row
The Esc key: also called "Escape" key, it's used to "cancel" things. It can close dialog windows, context menus, dropdown menus, and exit fullscreen mode in some applications.
The F1, F2, F3, F4, F5, F6, F7, F8, F9, F10, F11, and F12 keys: also called "function" keys, these don't do anything by default, and their functionality depends on the application, although some conventions exist, e.g. the F1 key generally activates a "help" function in applications that support it, F2 renames things, F5 refreshes views.
The PrintScreen key: saves an image of the screen. This function is provided by the operating system.
The Scroll Lock key: activates the "scroll lock" mode, which changes the behavior of some keys in a terminal emulator. This isn't very useful nowadays.
The Pause/Break key: the key is rarely used. It can pause a program running in the terminal on Windows.
Alphanumeric Area
Left Column
The Tab key: this is the tabulation key. It inserts in a tab character in text editors that support it.
The Caps Lock key: this activate that "caps lock" mode. While activated, the letters you type will be UPPER CASE BY DEFAULT INSTEAD OF lower case.
The Shift key: this is a modifier key that changes the behavior of other input while held pressed, but doesn't do anything by default. It makes letters you type UPPER CASE instead of lower case. If the Caps Lock is activated, it makes them lower case instead of UPPER CASE. If you press a key that has two symbols printed on it, one on top of the other, it types the upper symbol instead of the lower symbol, e.g. the symbols on top of the number keys. It changes the behavior of selection operations, such as clicks to select items in a list or clicks on text, to select everything from one cursor to the new position. It's also used in various keyboard shortcuts.
The Ctrl key: another modifier key that doesn't do anything by default. It's primarily used in keyboard shortcuts of applications, such as Ctrl+C, Ctrl+V, Ctrl+Z, Ctrl+Y, Ctrl+T, Ctrl+Tab, etc. The keyboard shortcut chords sometimes contain the Shift key, e.g. Ctrl+Shift+Tab.
Bottom Row
The WinKey: also called the Windows key, a modifier key that opens the start menu when pressed and released by itself without forming a chord. On Linux, it's called the Super key, Meta key, or Hyper key. This modifier isn't use by applications by convention, its shortcuts belonging to the operating system, e.g. WinKey+D.
The Alt key: a modifier key used by both the operating system and by applications. It doesn't do anything by itself.
The spacebar: types a space character.
On the right side of the spacebar, we have a right Alt key, right WinKey, and right Ctrl key.
The AltGr key: a special right Alt key found in keyboards of some languages. Its purpose is similar to the Shift key: it types the symbol printed on the right side of a key instead of on the upper part.
The Menu key: opens the context menu of the currently selected item or of the element with keyboard focus.
Right Column
The right Shift key, above the right Ctrl key.
The Return key. also called the Enter key, does two things: it confirms an action or activates the selection (the opposite of the Esc key) or inserts a line break (new line character) when typing a text. In a file manager, pressing the Enter key while a file is selected will open it, which is the same behavior as double clicking the file.
The Backspace key: erases a single character to the left of the text cursor (caret).
Navigation Area
The arrow keys: used to move the text cursor while typing a text, or to move the selection in a menu or list of items.
The Insert key: disables the "insert" mode in text editors that support it, switching to the "replace" or "overwrite" mode. While in "insert" mode, characters are inserted at the caret position. While in "replace" mode, typing a character replaces another character in the text, such that the total number of characters never changes.
The Delete key: erases one character in front of the caret while typing text (the opposite of Backspace). This key is also used to erase virtual objects that are currently selected in various applications, e.g. pressing the delete key while a file is selected in a file manager will delete it (and possibly send it to the recycle bin).
The Home key: while writing, moves the text cursor to the start of the current line. While selecting items in a list, makes the selection jump to the first item of the list.
The End key: while writing, moves the text cursor to the end of the current line. While selecting items in a list, makes the selection jump to the last item of the list.
The Page Up key: while viewing something that has scrollbars, makes the scrollbars move up exactly one "page." A "page" in this sense refers to the height of the viewable area the scrollbars are attached to.
The Page Down key: while viewing something that has scrollbars, makes the scrollbars move down exactly one "page." A "page" in this sense refers to the height of the viewable area the scrollbars are attached to.
Numpad
The Num Lock key: activates the "num lock" mode. While "num lock" is activated, pressing keys on the numpad will type the numbers. While "num lock" is deactivated, pressing the number keys won't type numbers, but instead they will behave like the arrow keys (8462, up, left, right, down) and home (7), end (1), page up (9), page down (3), and delete (comma).
The Enter key: the "enter" key on the numpad behaves exactly the same way as the "enter" key on the alphanumeric area. The only difference is that when the two keys need to be differentiated, the term "enter key" refers to the one on the numpad, while the one on the alphanumeric area is called the "return key."