Hello friends: 
 
Speak (produce language sounds):  
1.  "Speak up!"  
2.  "Don �t speak during the presentation."
 
Speak to (make an oral presentation, not requiring a response from the listener):  
1.  "May I speak to you about a private matter?"  
2.  "The politician spoke to the crowd."  
 
Speak with (have a serious one-on-one or intimate discussion):  
1.  "I will speak with you about that later.  Now is not the appropriate time."  
2.  "The principal spoke with the students about gang violence."  
 
Talk (produce discernible words orally):   
1.  He talks a lot.
2.  Don�t talk loudly.  Keep your voice down.
 
Talk to (have a back-and-forth conversation): 
1.  "I don �t want to talk to you."
2.  "Please talk to the teacher.  Explain the problem you´re having with the assignment."
 
Hope this helps.
 
Your American friend