In terms of tulpamancy, we define the act of proxying as listening for and repeating your tulpa's input to somewhere else. This can be typed, vocal, artistic, or anything else I can't think of off the top of my head.
Proxying in a single line is a very easy concept, but some people have trouble with listening for and fully understanding their tulpa's input. One of the main problems that I've had with Yt and Quora is that sometimes I think too loudly. Think about it as an audio mixer in your head with one channel dedicated to you and other/s to your tulpa/e. You need to turn your thought-volume down slightly and turn up the thought-volume of the tulpa you want to proxy for. Then all you need to do is relax a bit and type or speak what they say.
Initially, when you start doing a lot of proxying for them, there's a high chance that they'll send more unprocessed thoughts when they're making analogies and the like. If you're not sure what they mean or are saying, feel free to ask them what they mean and send back the thought to them.
This gets much, much easier over time, but initially it does feel kind of discouraging. Keep at it and you'll be transparently proxying for them in no time whatsoever.