hello friends.

suppose if i have to edit linux system files like /boot/grub/menu.lst, How can I make it possible?

How do i know where and how will i be saving that file?

does making changes affect instantly, how can i check?

thanks in advance

editing files is nothing amazing, feel free to do it (if you know what your doing), or first backup the original file then edit it (if your not sure)

anyway, as for when changes take effect, it all depends on the program

programs like lilo uses the config file to setup the boot loader, each time you want to update the boot loader (if you upgraded, or made a change to its config file) then you must run the program before it'll take effect

but for most, one should assume changes only take effect on program restart (as config files are usually read at startup of the program)

The configuration files are just plain, human readable text files. They are ment to be edited by humans in the first place.
Use a text editor for editing them. Generally, you want to save them on the same location where they were before.
And of course, you should back up the original file before editing (in case you break it, you can restore the backed-up version).