some times using for& to ,it become doubtful

For ... 1) to indicate the reason or because of — I am really happy for you. 2) to indicate the duration or time— I attended the session for one year only. 3)specify the use of something— She is preparing for her final exam.... To..... To is a preposition and a versatile little word that can be used to say many things. You can use it... 1)to indicate a goal.. a direction of movement.. you say you’re going to class tomorrow.. 2)as well as a place of arrival... 3)You’ll often use to when you want to indicate a relationship between words, relationship like possession, attachment, and addition. You get attached to people, you have things that belong to you.  4)To is also used to indicate a range or a period of time, like when you say it will take you five to ten minutes to finish something

Uses of "TO" 1. Destination: (I'm going to Paris) 2. Time: ( It's quarter to 11.) 3. Distance: (I have to walk 10 miles from my home to university.) 4. Comparison: (I prefer sleeping to working.) 5. Giving: (I gave my book to my friend.) 6. Reason with verb. (I came here to help you.) Uses of "FOR" 1. Benefits: (Exercise is good for health) 2. Schedule: (I made an appointment for May) 3. Agree with: (Are u for or against the development) 4. Doing something to help someone: (Could you carry these books for me ?) 5.Reason with noun: (Let's go out for a drink.) 6. With v1 + ing form: (A big spoon is used for serving this soup)