1.Purpose:We use to/in order to/ so as to/ (for sb) not to/ so that/....
Examples: We had a meeting today so as to discuss next year's programme.
He did all he could for her not to worry.
I moved to France so that I could improve my French.
Everyone did their best in order to finish the work.
2.Reason: We use since/as/because/ owing to/ thanks to/due to/ because of/ as/ for/ seeing that/ ....
Examples: Since you don't believe me, I won't give evidence.
Because of his lack of training he had difficulties finding a job.
On account of the weather we didn't go for a walk.
Billy was punished for lying to his teacher.
Owing to the snow,the planes couldn't take off.
As you are a foreigner you can't express your opinions on the situation in the area.
Seeing that you aren't interested I' ll do it by myself.
3.Result: We use so/ therefore/ as a result/ consequently/ as a consequence/ ....
Examples: He missed the early train, as a result he was too late for the job interview.
The result of his trial, therefore, could hardly have been other than a foregone conclusion.
If he locked the door, then Kitty is trapped inside.