Writing a offer for the 1st time

[Ernes Sahic]

I found a property being sold by a investor who can't handle the extra property, so she is selling it. She is asking 60k, after looking at the property and running numbers on the BP calculators. I'd like to make a offer of 53k. This is my first deal and I've never made a offer. Looking for advice on how to make a offer. Is it as simple as just calling and making my offer over the phone and explain why I came to that offer or do I need to write out a offer with a contract?