I am Using smith chart to measure and optimize S11 or Return loss for my antenna.When I put markers on required resonant frequency say 2.44 GHz I get some curve and In marker stats (Format : Resistance in ohms, Reactance in ohms , inductance or Capacitance ). How do I optimise the return loss using these Marker stats.

Attached is image for your reference

You would be better attaching a Touchstone file. But looking at your Smith Chart, there are least 5 resonances (probably 6 or 7, but hard to be sure), although only one is close to 50 Ohms. If you look at the frequency at the one near the centre of the screen, then that is close to 50 Ohms. If that figure was at for example at 3 GHz, and you want it at 2.44, then scaling all your dimension by 3/2.44=1.23 would be worth a try.

If not you can create a matching network, and match whatever impedance you get at 2.44 GHz to 50 Ohms. HOWEVER, if the impedance at 2.44 GHz is far away from 50 Ohms, that is not practical.

I don't know how good it is, but there's one online matching network calculator here:

https://home.sandiego.edu/~ekim/e194rfs01/jwmatcher/matcher2.html

Make sure you measure the impedance at the point where you will put the matching network. If you measure the impedance on a bit of arbitrary length of coax, and intend fitting the matching network close to the antenna, then it is not going to work properly.

In addition to impedance matching, you need to consider whether the radiation pattern of the antenna is what you want. You could build a 10 element Yagi-Uda antenna at 100 MHz, and match it at 2.44 GHz. However, it would not make a very good antenna, and would be excessively large!

Have you considered modelling the antenna? There's a huge range of software available. For wire antennas, the free MMANA-GAL at http://hamsoft.ca/pages/mmana-gal.php is worth looking at. For really complex things, things like EMPRo or HFSS are needed, but each will cost more than a modest car.

There are whole books on antennas, from those aimed at amateur radio, to professional books by authors like Krauss, Jasik, Volakis, Balanis and others. Unfortunately, antennas is a very complicated topic, so the professional books tend to be very heavy on maths.

For a WiFi antenna, a helical antenna is worth considering. You make the circumference equal to the wavelength, and a pitch of about 12 degrees. They have an impedance of about 140 Ohms, so quite easy to match. One way to do that is to make the last 1/4 of a turn into a transmission line of an impedance of about sqrt(50*140)=83 Ohms.

BTW, there are tons of videos on YouTube about helical antennas. Most are totally useless. This one

https://www.youtube.com/watch?v=7GWoAUM2mAs

in particular is amusing for the stupidity of the author. I think YouTube is just a magnet for idiots making videos on subjects they know nothing about. There are some comments by "Dr. David Kirkby" on the YouTube video. Those are my comments, so you can see what I think of his antenna!

Dave