Hi Izzati,
You can Ctrl-click on a specific atom to select it.  This is called "picking"

The user guide explains how you can select things:
<https://www.rbvi.ucsf.edu/chimera/docs/UsersGuide/selection.html>
<https://www.rbvi.ucsf.edu/chimera/docs/UsersGuide/selection.html#pickselect>

There are several tutorials, including some for beginners, if you want to learn more about Chimera:
<https://www.rbvi.ucsf.edu/Outreach/Tutorials/GettingStarted.html>
<https://www.rbvi.ucsf.edu/chimera/current/docs/UsersGuide/frametut.html>

I hope this helps,
Elaine
-----
Elaine C. Meng, Ph.D.                       
UCSF Chimera(X) team
Department of Pharmaceutical Chemistry
University of California, San Francisco

> On Oct 23, 2020, at 7:54 AM, Izzati Mokthar <izzati5676@gmail.com> wrote:
>
> Hi, I am Izzati.
>  I would like to ask how to select only one water molecule in chimera?
>
> Thank you