Just like you can paste a note on a sheet of paper, you can paste data into a document on a computer. The paste function can be used to paste copied data into text documents, images, Web browser address fields, and just about any place where you can enter data. However, to paste data, you first need to copy it to the "Clipboard," which is a temporary storage area in your system's memory, or RAM. This is done by first selecting the data you want to copy and then choosing "Copy" from the program's Edit menu.
Once you have data copied to the Clipboard, you can paste it within the same document or within a different document in the same program. You can even paste copied data into a document within a different program. However, you can typically only paste data into a document with the same kind of data. For example, you cannot paste an image into your Web browser's address field or an audio file into image editing program.
To paste a copied piece of data, select "Paste" from the Edit menu in the program you wish to paste the data in. Text documents or programs with text fields will typically paste the data wherever the flashing cursor is. You can also use the keyboard shortcut "Control-V" for Windows or "Command-V" for the Mac OS to paste the data. The reason the "V" key is used is because the "P" key is usually reserved for the "Print" shortcut and "V" is right next to the "C" key, which is used for copying. So it might not be that intuitive at first, but it makes sense when you think about it. =)
For more information about copying and pasting, view the Help Center article.