Interest Groups (IGs) are self-organized teams on Discord that meet regularly to dive deeper on specific topics. Once you are on the MLC Discord, you will see a category named "INTEREST GROUPS" within which you'll see a number of channels. For example, this is a screenshot from 3/2022:
To join an Interest Group, you simply go to the corresponding channel and state your interest. You will have to react to this message to set up your automatic notification, but don't worry if you don't know how to, folks in the channel are generally very helpful.
To start an Interest Group, that is, if you find the need to start learning about one topic and wanting to attract peers to do it together with you, and such topic does not already exist in the list, here are the steps to do so:
#generalthat you are interested in starting this thing, see how many people respond
INTEREST GROUPScategory for you and make you a MOD (ask in the
#ask-an-adminchannel if needed)