This is a one of many mini-posts that I will do on using the VI editor. I've recently bumped into some pages that contains valuable information on how to use VI. The problem with it is its too wordy and that makes it hard to look for information when you need it.
So this post and the following ones will use tags relevant to the subject to help the search for relevant information quicker.
D - delete the characters of the line after the cursor position
C - delete the characters of the line after the cursor position and change to insert mode
R - change to insert & overwrite mode; it's like pressing the Ins key on the keyboard; whereas ‘r’ replaces a single character, ‘R’ replaces every character that you type over
s - behaves like ‘x’ but switches to insert mode
S - deletes the whole line and change to insert mode