If file is already opened in normal mode
G goes to the end of the file
o enters insert mode on a line below the current one
If you are opening the file from the command line
You can open vim on the last line of a file from the command line using:
vim + filename
+ lets to specify the line number. Leaving it blank defaults to the last line of the file as explained in the man page:
+[num] For the first file the cursor will be positioned on line
"num". If "num" is missing, the cursor will be positioned
on the last line.
Then you can use
o as above to enter insert mode on the line below.
What about inserting at the top of the file (or an arbitrary line number)?
In normal mode
gg can be used to jump to any line in the file by number. So
5gg jumps to line 5. gg without a number is a shortcut for the first line of the file.
If you wanted to insert a line above the first line, you could do that with: