For & To

Their uses and differences

We use for when someone derives benefit from the action.
We use to when the objects moves in the direction towards something or someone such as in the following examples.

• Alex bought a horse for Nastya - Nastya derives benefit from Alex's actions. 
• Nastya brought the horse to the drinking through. The horse moves to the trough. 
• Alexey made a bomb for Elena. Elena gets the bomb and some benefit from having it. 
• Daria made a cake to Lyuba. This is ungrammatical but if we use a verb of movement like give or sent or brought then it becomes correct. 
• Daria baked a cake and sent it to Lyuba. Alex gave a kangaroo to Yana (The kangaroo moves to Yana. 
• I wrote a letter for Daria. Daria benefits as I did the work of writing the letter for her. 
• Nastya wrote a letter to Matt (The letter moves towards Matt. 

D: Hi Matt, what are you doing?
M: I'm writing a letter to someone.
D: Who is the letter for?
M: It's a letter for the Whatsapp group, I will send it to the group in a moment.
D: What is the letter for?
M: It's about the new website.