How do I get my pictures to look like this?

alot of practice,lessons and equipment :3

practice, practice and even আরো practice! I can't do it like that (yet) and I always get so frustrated ^^"

Well of course lots of practice and also that pic looks like the person drew it on the computer so it depends on how well আপনি can draw on the computer, what system they used like Paint sai অথবা Photoshop.
When আপনি get the hang of drawing the colouring is different because there's many ways of colouring and shading.
Also আপনি could go on ইউটিউব and look at tutorials অথবা speedpaints to help আপনি get an idea of how to and keep trying you'll get there sooner অথবা later অথবা something like that because everyone has their own kind of art style

they probably have the help of a computer....

practice.