Ladies will have mood swings... pains... during periods... how should a husband behave or what all things he can do to support her...

It's wonderful that you are giving it some thought and consideration! Some women do have a more difficult time with their menstruation than others. How would you treat her any other time that she is not feeling well? It would really be no different.

If she is experiencing considerable pain, you could offer to get her a heating pad, and perhaps some pain medication, for example. Prepare a meal if she is not feeling well. If you have young children, occupy their time so that she can have a bit of a break.

She may be fine and not have any real discomforts, but just asking if there is anything she would like you to do or that you can get for her would be considerate if you know she isn't feeling well.

30 years ago I used to take dolomite, a natural mineral put in pill form, and it helped me. Also the usual pain relievers such as Tylenol and ibuprofin. I had less and less discomfort the older I got. (Now I have others.. )
Yes, definitely a heating pad. Long underwear if cold weather. It can feel better to have something tight around the abdomen like synthetic stretchy long underwear.
Lying on her back and lifting her pelvis for several seconds, over and over, propping up her body with her hands.
Avoid constipating foods and caffeine and drink plenty of fluids.
Walking.
Hug, hold, and snuggle her, every day and night.

Just doing the small things can really help, for example, make up the bed with fresh linen,if you have children maybe uping the anty a little,example,take then out of the house for a hour or so if possible.

As bad as some women suffer from cramps many forge through and get on with their lives.

Try not to take anything too personally and have patience.

Well first of all that is so nice of you to think about this and also to try to help! XOXO!
Well I will tell you what I would like my hubby to do:
1. be very patient and no matter what tantrums occur just kiss her and do something cute like give her a flower or a sticky note saying I love you!
2. ask her if she needs massage, neck and back would really help
3. make her feel cozy with hugs and a warm tea and cuddle her in a blankie
4. if she is in severe pain get her a Midol and ask her in what other way you can help
5. bring breakfast in bed
6. give her privacy is she wants it
7. at least this time of the month help with household chores and kids, because she may really feel tired, sick, in pain and miserable enough not to want to do any of those chores