Straightning hair-

When I straighten ma hair--its straight--buh when I go outside ---windy or not windy---it start being wavy again---
What should I do to keep it striaght?

Nothing to do with wind, It's humidity and summers are really humid

put hairspray in it to make it stay like that. or you have to carry around a brush and when it begins getting wavy brush it.
its usually because of the humidity where your hair gets poofy or wavy again.

I have naturally wavey hair and when I sraighten my hair I use sunsilk straighten out shampoo and conditioner. in the morning when I straighten my hair I put hairspary on it, not a lot just enough to make it stay in place.

THERES A STORE CALLED SALLY BEAUTY THEY SELL A HAIR PRODUCT CALLED SILLICON BUT IT THAN PUT A SMALL AMOUNT ON YOUR HAND ABOUT THE SIZE OF TWO SKITTLES AND RUB IT ON YOUR HAIR! HOPE I HELPED

Go for Rebonding

All I do is use an anti-humidity spray before blow-drying and straightening my hair, and then when I am going to head outside I throw it in a low bun until I am in the car/house wherever.

if you want to keep it straight do what the above people have said
but if you ask me your fine with wavy hair,
if you mean wavy as in curves then I'd keep it like that, it looks good on you