How do you know when to use SHIFT+INSERT vs CTRL-V vs right-click-paste to paste?

There are two types of clipboards in Unix/Linux: PRIMARY (often used with Ctrl-X/C/V) and SELECTION (mouse selected text, inserted with Shift-Insert or clicking the mouse middle button).

See https://wiki.archlinux.org/index.php/clipboard for more details.

Here's what I used to do:

Ctrl+Insert : Copy to the clipboard

Shift+Insert : PASTE from the clipboard

Shift+Delete : Cut TO the clipboard

Now I have an Apple Keyboard, I do: (The apple keyboard does not have an insert key)

Ctrl+C to Copy to the clipboard

Ctrl+V to PASTE FROM the clipboard

Shift+Delete to cut TO THE clipboard.

In a terminal using Putty:

Select the text with the mouse copies directly to the clipboard

Right-Clicking anywhere in the terminal window does the paste

In a regular shell session:

I select with the mouse, and use Ctrl+Shift+C to COPY to clipboard

I use Ctrl+Shift+V to paste.

This question seems to be related to the behaviour of keys combinations, but you don't give an application in which you perform these keys combo. So, taking in consideration what Javier Rivera says, the reason of why it is needed to use SHIFT+CTRL in a terminal, is because of some of these combinations are used in terminal command's control.

In example: when you wish to "cancel" the current command, you pŕess CTRL+C, which is used in the majority of the systems to perform the "Copy" task. This way, if you press CTRL+C in a terminal in order to "Copy" a portion of text and an application or process is running, you will "cancel" the process or "close" the running application.

Depending on the GUI that you use, or the software application itself, SHIFT+CTRL is useful for formatting or performing the "special-paste" task, which allow you to choose the format on which the copied text will be dropped into the application.

In example: if you use OpenOffice Word Processor or Spreadsheet, when SHIFT+CTRL+V you will be prompted to choose what format will you use for the clipboard to be dropped into the document.

The next image illustrates how the CTRL-V and SHIFT+CTRL+V keys drops the clipboard's content into a document:

The next image illustrates how the CTRL-V and SHIFT+CTRL+V keys drops the clipboard's content into a document, AFTER CHOOSING THE FORMAT in the right side documen:

In certain cases, as code (html, php, javascript) editors, you can choose between pasting the portion of text copied from a website or the code that generates the text in the website. In example: when copying from a formatted table, you can choose to paste the text in the table or to paste the code for generating the table into a web.

You should check into the application's "Edit" menu in order to see how the "Paste special" task is handled.

The next image illustrates how OpenOffice Word Processor handles the "Paste Special" feature: