Unfortunately it's still a very weak type of blocking, for you on Lemmy.ca unless you are using an app like Sync or Connect. It's basically a "community mute", equivalent to unsubscribing from all the communities there individually, but unlike user blocking, the users from that instance will still show up in other communities, they can still send you replies, which will trigger Notifications, and therefore they can harass you by continually sending you replies for WEEKS and WEEKS at a time (this actually happened to me twice, once with hexbear.net and another time with lemmygrad.ml).
Anyway, it's better than nothing!
You may be interested to read some of the ways that PieFed is advancing democratization of moderation.