how can i make a tesla coil

Do you mean, say, as a block, or as an entity? 

Either way, you can use an entity iterator bracket to target entities within a certain range. You would probably want to use some sort of projectile attack, which would be easier to program for an entity than a block, but either method is possible. Instead of an entity iterator, you could also try using the 'does entity of [type] exist in radius' function, along with the 'nearest entity of [type]' function to target one entity at a time, and prioritize the closest.