All correspondence chess sites that I've played on allow players to refer to databases of human games and chess books while they're playing a game. I'm assuming that this is OK here as well, but I just wanted to check. I searched the FAQ, but wasn't able to find anything about this. I think that it is important that this is made clear. It was quite a while before I learned that this is part of correspondence chess, and it would have been good to know this from the start.
At the bottom of the page is a link to "Terms of Service."
If you read it, you will find this in section 3. (b).
While a game is in progress you may not refer to chess engines, chess computers or be assisted by a third party. Endgame tablebases may not be consulted during play but you may reference books, databases consisting of previously played games between human players, and other pre-existing research materials.