How do you get high blood pressure?

Heredity and aging. For most people it's genetics and getting older. About 10% of people have another cause. The most common is any form of kidney disease. Rare tumors can produce hormones that raise bp. Rarely, a narrowed renal artery is the cause.
Many causes. That is a very broad question -- most common cause of intermittent elevation of BP is stress usually mental or emotional more than physical stress -.