Copy :
Step 1: Change mode to "Visual Mode" :
Start Visual mode line wise : Esc + V
Start Visual mode per character : Esc + v
Step 2: Yank lines with visual mode line (character with visual mode per character) you want to copy with command:
Y : yank current line(character)
nY : yank n lines(character) from current line(character)
Paste :
Step 1: Move cursor to location, that you want to paste
Step 2: Use one of two commands:
p : paste below cursor
P : paste above cursor
Example : i want to copy line int ret; and paste below line int randomvalue;
Step1: Move the cursor to line int ret; then start Visual mode line wise : Esc + V
Step2: Press Y to copy line int ret; then move the cursor to line int randomvalue; and press p