Problem with meta description

Hello, I shall want to know where then I to put meta one description, on which file and where is t he(it)?
Have to I install(settle) a plugin?

Because the description of my site is not adapted, she(it) corresponds in fact to one of my articles

http://image.noelshack.com/fichiers/2014/49/1417688299-descri.png

http://image.noelshack.com/fichiers/2014/49/1417688302-descript.png

My website : http://tourbilol.com

Thanks