I really dislike when clients expose the relay settings as "read" and "write"... Those words make little sense to users. 

In the context of the Outbox model, write is where your posts are located and read is where people send you their posts for your notifications. 

Your client is "reading" from both at all times. It reads from the "write" relays to get your posts, and it reads from the "read" relays to get the replies to your posts. It also writes to your "write" when the post is yours, and writes to everybody else's "read" relays then they are tagged in your post.

On Amethyst, we use the words "home"/"outbox" for "write" and "inbox" for "read". I don't know if those are the best words, but it seems to make things a little easier to understand.