Walking into a room full of strangers can be intimidating. The best thing you can do is think about what you need to accomplish here, what are your goals? There is no point trying to strike up a conversation with people who potentially cannot help you.
You mention you know the host, ask them to introduce you to key people, this might not always be possible so you should think about setting yourself an objective, like speaking to 3 new people. In terms of knowing what to say, you could just make a comment about the venue or ask how they know the host? You should maybe focus on asking questions to open the conversation.
It’s not easy but just walk up to someone and ask them, how you doing? Shake their hand and introduce yourself. It’s a challenge but if you manage to do it once, the second time will be easier.
