IBM 3270 User Manual page 45

Use the Insert key (which you are already familiar with)
to insert the word "last" into the following sample sentence.
Sample Sentence: This is the time.
Insert it just in front of the word "time".
The Backspace Delete key is marked by an arrow that points left.
(See Figures 2-1 through 2-4 to help you locate the
Backspace Delete key.)
After you type the word "last", press
the Backspace Delete key to undo the insertion.
Every time you press the key, you delete the previous
character and back up the cursor by one position.
Remember, this function operates only while insert mode is set.
We also need to understand how word wrap works when insert
mode is set.
Do the following for practice:
Turn on insert mode and make sure that word wrap is on.
Insert enough words into the first sample sentence below
to force a word into the right margin and see how word wrap
works in insert mode.
Sample Sentence: This is a sentence.
This is a sample sentence.
The words wrap out of the first line into the second
line as long as there are sufficient spaces or
nulls on the second line to accoiranodate them.
When the next line cannot acconmodate the word, the
keyboard locks.
Now let's try the cursor position indicator function.
Press the CURS POS key.
The current position of the cursor is displayed in the
bottom row of the screen in the form rr/cc.
The letters "rr" mean the number of the row.
The letters "cc" mean the number of the column.
The rr/cc value remains displayed as long as you hold down
the ALT Shift key.
Remember that line formats (margins, tab settings, and an
"end of line" signal setting) are remembered as long as power
remains on at the control unit.
5-8 Entry Assist User's Guide