Ok. I played with this a little bit and I think I get what's going on.
A decoction step assumes you are drawing some amount of the thick wort off, bringing it to a boil and adding it back to the mash to reach a specific temperature. In this case, the "Amount" column is telling you how much wort to draw off.
A temperature step is assuming a direct fired mash tun and is there so you remember to fire the mash to a specific temperature.
An infusion step assumes you are adding some volume of water to the mash to raise it from temp A to temp B.
Your first step, the acid rest, is an infusion step. Beyond that, I am really not sure what you are trying to achieve or what equipment you have. If you are really wanting to do a decoction mash with the volumes shown, you need to draw 4.75 gallons of wort off, bring it to a boil and add it back to the mash tun. If you do not have 4.75 gallons of wort to draw off, you may want to consider raising the temp from 97F -> 133F with another infusion step, and then doing a decoction mash to raise it from 133F -> 155F.
Most of this is a guess, because I don't know your batch size, what amount of grains you are starting with, etc. If I haven't helped, open a bug on
https://bugs.launchpad.net/brewtarget and attach the beerXML for your recipe. I will take a look and try to explain better.
