Often times how they communicate and/or how we understand them is not through words, but through instinct, gut feelings, simply knowing what they mean, etc.
There are more developed forms, but starting there is easiest for most people.
Would also like to add ,find a good development circle where you can sit study and learn.
Not all mediums work in the same way we all have our own unique style and way of connecting to spirit. Find a mentor that you connect with. Go with what feels right for you.