Which is good image editor or graphics drawing tool for Linux? What is the Ubuntu equivalent of MS Paint?

There are several tools available for Image drawing or editing , graphics design: GIMP, xpaint, gpaint, kolourpaint, mtpaint..

GIMP or General Image Manipulation Program is one of the most popular and good graphics editor.

GIMP can do image editing tasks such as resizing, editing, cropping , converting between different image formats. 

To instal on Ubuntu, open terminal and type command:

   $ sudo apt-get install gimp


Tip: If you are migrating from Windows to Linux then KolourPaint from http://www.kolourpaint.org/ may be a good choice.