:Hi there. The guidelines for this are located at WP:Articles for deletion discussion guidelines#How to contribute. If you click on the link (Wikipedia:Articles for deletion/Reekrit Serai), it should take you to a deletion discussion. On that page click the edit tab next to the article name, which should open the page for editing. Go right to the bottom of the edit box and put your comment in. The text you type should be as follows: 
 ::*'''Delete''' - followed by why you think it should be deleted. 
 :Often editors include links to relevant policies like WP:AUTHOR and WP:BASIC, which one editor has already highlighted. Alternatively you can just have "*'''Delete''' per nom." which just means that you agree with the reasoning given by the nominator. Hope that helps but if not, feel free to ask me.