Slack has channels and direct messages. When speaking to one or two people directly when there is no need to include others or allow them access to the discussion (think about the specific conversations that happen at work where saving the information and making it available isn’t necessary). This is where direct messages come into play. But for broader conversations channels work great. And channels are the main place where conversation happens.
You can create both private (locked channels by invitation only) and public (any member of your Slack can join). Side note: no one outside of you Slack team can join anything that you have created. This is a secure messaging app that requires logging in. We have created multiple channels that separate conversations in the various spheres of ministry. We have public channels for missions, children, music, and prayer among others. We also have private channels for our pastoral team, deacon team, finances, and documentation. This allows us to speak to issues within each ministry sphere and reference the conversations later with ease. Here is an example, but set it up however works best for you.
There is also a general and random channel that every Slack team member is automatically a part of. These channels are exactly what they sound like. General work and church conversation takes place in the general channel. The random channel is where we can goof off a bit, just the way that you would at the office from time to time.