You can re-use a piece of text in another part of the file by yanking it into a temporary buffer and then putting the contents of this buffer back into the file.
The command y yanks the text into the temporary buffer.
Combined with other commands that are used to move around text objects, the yank command can be used to pull any part of a file into the buffer.
The command p pastes the contents of the temporary buffer back into the file immediately after the cursor.