“Therefore” is very similar to “as a result.” Something is a fact, and after thinking about this fact, you can make a conclusion. It sounds a little formal in everyday speech but not uncommon. The word “therefore” is frequently used when writing.
His skin burns very easily; therefore, he’s decided to stay under an umbrella and wear lots of sunscreen.
Our lives have become too complicated; therefore, we’ve decided to simplify things and move to a log cabin in the country.
He spends too much time doing office work–even when he’s out with his girlfriend; therefore, she’s thinking about ending the relationship.
There were too many accidents on this road when the speed limit was 55 miles per hour; therefore, the city decided to lower it to 45 miles per hour. The limit for snowmobiles was also lowered.