I've heard of Bougainvillea been used in tea's to help reduce stomach pain. It's also great for when you have a sore throat or a cough. Those are the only two things I know about, however, I am sure that someone else on the site can help give you a better understanding of what it can be used for.
Bougainvilleas grow all over where I live and like Vozel said, they help a lot with sore throats and coughing. I'm sure there are other ways to use it, but one method my family and I use is turning it into tea. To make it, all you need is one cup of bougainvillea petals and two cups of water. You bring the water to a boil (while it's coming to a boil you can add a cinnamon stick or two to increase the flavor), add the flowers for two minutes then remove them along with any cinnamon sticks you might have added. When it's finished you can also add a spoonful or two of honey to it; that would further enhance the teas taste and effectiveness.
I second Vozel and Goldiana.
You can also use the Bougainvillea leaves to help with diarrhoea. The stem and the roots can also be used in teas.
But I need to warn you, Bougainvillea can be mildly toxic for children. So, it is adviced that you only use it as tea and use small proportions of it, due to its toxicity. As soon as you feel nauseous stop using the plant.