Its very easy!
You do not want to add coffee ground directly to the wort or beer, it will extract some of the oils in the roast coffee beans that impart a bitter/harsh taste that is not very pleasant. This is why brewers will mainly add cold press coffee into their beer, steeping the coffee at cold temps will extract the flavor, but not the bitterness from the beans.
Here is how I do it. You will need a quart mason jar with a lid. Boil a cup of water and pour it into the mason jar and cap it, turn it upside down to ensure the water makes contact with the lid as well to help with the sanitation of the jar. After a few minutes, stick it in the fridge and let it sit there overnight to let the water cool down. The next morning, add a 1/3 cup of coarse ground coffee beans to the water. Shake a few times to incorporate and stick it back in the fridge for 24h. Use a cheesecloth or coffee filter to separate the coffee grounds from the liquids and you then have cold press coffee.
You can add this at any point (boil, fermentation, secondary) but I prefer to add it at kegging. Some add it at the end of boil for sanitation reasons but I feel confident enough that the boiled water and alcohol in the beer will be enough to keep the other things at bay. If I were bottling the beer for long term storage, I would add it at the end of boil just in case.
Report back and let us know how it turns out!