getting env_explosion to work

I am trying to make a mine,ive been told to use env_explosion, but can't find any way in its properties to make it trigger, anyone know how to make from env_explsion or any other way i am supposed to do it?

Set your env_explosion (give it a name like explosion01) on the ground, then draw a brush around it with a trigger texture. Tie the brush to trigger_once (call it trigger_explosion01). In the outputs, set OnTrigger to Explode your explosion01. Your flags should be okay by default, as you want just players to set it off...but you can always set it to Everything, if you want people to be able to throw stuff across the field to set off the mines.

thanks

sorry to bring up old thread, but is there a way to make it so random explosions happen with out a trigger,like mortars landing? thanks

make a new post for a new question... but... just make a longic_timer and set it to fire randomly.

thanks