Sudoers list
 

It would be a great help if someone help me to add my user in sudoers list. I have already created user using adduser command.

You need to edit your sudoers file in the appropriate way. You can find one explanation here. A quick search on the web will find you plenty of other explanations. You'll need to use visudo to do the job.
jdk

My preferred option is to use a group for this:

Then add the relevant user to the group
Then modify the sudoer file to allow this group to run any command add the following line with /usr/sbin/visudo

Now that you've the group set up you can add or remove the user from the group accordingly.

Note that in this example the user will be able to execute ALL commands but will have to use their password to execute them.

How to add line with visudo
 

I tried to edit visudo using text editor like mc but failed. The output of
/usr/sbin/visudo
only displays the contents

running visudo lets you edit the file with "vi" commands, go read up on man visudo

Don't edit the file using visudo... You need to learn about vi and I remember my first passes at vi... I broke the script I tried to edit :P

use one of these commands (as root):or any other text editor you feel like using (but I don't know any editors more "user-friendly" in cli)

Just make sure you understand what you need to add and don't go for the no password option...

P.S. Just in case you are curious what's all the fuss about vi/vim.. type in a terminal emulator when you have some spare time ;) The worst case scenario, you just learn something new ..

nano is my favourite simple editor.

+1 :)

You can use any editor you like with visudo using the EDITOR environment variable, e.g.:

Will replace vi with nano when visudo is run.

Just typing visudo as root takes you directly to /etc/sudoers at 1 time in debian it was almost like using vim but now when I use it the interface is almost the sam as nano.

Hi,
Do not do this. visudo will make sure the file is locked correctly and check for syntax errors. If you don't like the default editor used by visudo, then set your EDITOR environment variable to an editor that you do like.

Evo2.

So doing the following
followed by will give you a better visudo experience.:)

nano /etc/sudoers

or add yourself to the wheel group and uncomment wheel

Hi,
visudo, vipw and vigr exist for a reason. Feel free to ignore them at your own risk, but don't encourage others to do the same.

OP has not stated what distro this is on so there is every chance the that wheel group doesn't even exist on this system.

Please be careful when offering advice.

Evo2.

@evo: I actually never knew (or never took to much care to notice) that the EDITOR variable existed.. Thanks..