The Hammers embark on their first campaign in a major European competition since the 2016-17 season and will be joined in their group by the Croatian champions as well as Genk and Rapid Vienna.
Speaking to the press ahead of Thursday's trip to the Maksimir Stadium, Moyes has admitted his side lack experience at this level and they will need to "respect" Zagreb on their home turf.
"This is new to us, but we have watched Zagreb and we are very much aware of their history, we saw their performance against Tottenham Hotspur which was very impressive," Moyes said on Wednesday evening.
"I don't think Zagreb will see us as anything different so they will come into the game confident. This could possibly be the toughest game, away from home, but we go into it with a fit group of players.
"You need to gain experience so that is why we need to give respect to Dinamo Zagreb who have been regulars in European football, we are still relatively new to the challenge.
"We have tried to take everything on positively and forward-thinking, we will try and be aggressive in our own way but ultimately we know we are new to the competition. [I hope] we will get to understand it the longer we go in the competition."
Moyes also stated to the press that every player in his squad is fit and available to play on Thursday, with a strong starting lineup set to be named by the Hammers head coach.