Structure

Alright so now I think is a great time to talk about the structure and replication of DNA. First, the structure.
DNA Structure
Here are a few basic things. 
DNA is made from nucleotides linking together. Each nucleotide is composed of three different structures: a phosphate, a sugar, and a nitrogenous base. The phosphate and sugar make up the sugar-phosphate backbone of DNA and are the same throughout the DNA structure.  The nitrogenous bases are those lovely ATGC letters we connect to DNA. (Just a reminder A is adenine, T is thymine, G is guanine, and C in cytosine. Adenine and thymine pair up and guanine and cytosine pair up.) With that knowledge click here to practice pairing bases.
There are so many other little details, but I think we should stick to the basics. So, here is another link that shows how nucleotides are added during replication. It's a video and it's pretty cool. Have fun!