I don't look at anything until I get it on the computer. By then, there isn't a whole lot you need the histogram for.
The histogram shows you the exposure.
The right side is the highlights, the left is the shadows.
The top is more data, the bottom is less data. If part of the histogram goes off the top of the graph, that area is either completely blown out or so dark that there is no detail - depending on what end of the histogram it's on.
If the histogram is mostly on the left side, you likely have an underexposed image - most of the data is one the dark end of the graph.
Bracketing is when you take multiple exposures, at different settings.
With IR, it's often hard to know ahead of time what your settings need to be. You can't see anything, and you can't use the meter either.
Say that the "good" exposure is 15 seconds. You might want to bracket that by one stop and take an additional exposure of 8 seconds (one stop under) and 30 seconds (one stop over).
I'll usually start at 5 seconds and take additional exposures at 5 second intervals up to 30 seconds.