He is the patron saint of Scotland and our flag is St Andrew's Cross because he was crucified but felt unworthy to be nailed in like Jesus, so he asked for a cross X. He was one of the original 12 disciples they say and he travelled the world spreading the word but didnt actually reach Scotland. His relics were brought here by some other guy.
St Andrews day actually originates in your country. Americans with a Scottish heritage began celebrating him. Then when we got a government that was solely Scottish they gave us the holiday
We don't do anything. It's not like St Patrick's day. Some of the smaller villages will have a Ceileigh, but basically it's just our way to reassert our unique identity in the UK.