The AfD format is used by convention - it's nothing official. Note that the AfD process is a discussion, not a vote; the closing administrator will take into account the weight of policy-based arguments. Therefore, it is important to explain your reasoning with reference to policy. The 'standard format' (as I say, convention, not policy or law) is to put;
*'''Delete''': I can't find [[WP:N|significant coverage]] for this.~~~~ *'''Keep''' This is really cool! [[User:Example|Example]] ([[User talk:Example|talk]]) ~~~~~ :'''Comment''' This is not a valid reason; please see [[WP:ILIKEIT]]. ~~~~
This would appear as;
If you wish to participate in AfD discussions, the best way to learn about them is simply to join in discussions - be bold, and have a try. You can always get there quickly by typing WP:AFD into the search box. Cheers!