I find that "to" and "and" sometimes can mean basically the same:
I went to the mall and bought some milk.
I went to the mall to buy some milk.
To me,there are little difference between them when it comes to indicating a purpose,and they both can be applicable to answering a question like:"what did you do last sunday?"
The only thing come to my mind about their difference is the first one the two verbs"went" and "bought" are equal level and both modify the subject "I", whilst the second one the "buy some milk" is subordinate to "went to the mall"
Well,I don't know exactly,maybe you can help me to tell which to use in what contexts?