Creating See Through Grates

I am very new at Doom Editing and I am currently using doom builder. I wanted to make a small room with a grate texture infront of it but when I inserted it the texture showed up but in between the bars is black solid. I cant see through them. How do I make it transparent in between the bars?

You need to have a sector on both sides of the linedef where the texture is.

:)

I understand a little but can you explain a little more? Sorry I am still learning the ropes lol

Do the following:

1. Create two adjacent sectors.
   
2. Find the linedef that is separating them.
   
3. Set the middle texture on this double sided linedef.