Sorting Type

On lemmy.world at the very least, posts are sorted by default to "Active". Active will decay posts based on the popularity of its most recent comments. This keeps the most discussed topic on the front of the page, and they'll stay there until people stop talking about it. This also makes it possible that a "dead" thread can get revived if enough people newly discover it & comment on it. This is a very valuable feature, but for us content junkies it may not be your desired default.

Switching to "Hot" will decay posts based only on their age & popularity (not their comment's age & popularity). When filtered to "Hot", you will see a lot newer, less-popular (but more current) content. The decay doesn't seem to be tuned to how a lot of us may be used to - it's more of a "Rising" than our typical "Hot" - but nevertheless it at least gives a constant stream of semi-popular new content.

Sorting Scope

On lemmy.world at the very least, posts are filtered by default to "Local", which only contains communities created on lemmy.world.

If you switch your default to "All", you will open up your content stream to everything within the fediverse. Warning: this does include NSFW content & communities (but if you are OK blanketly removing NSFW content, you can disable it in your settings)

If you are having trouble grasping the concept of "Local", "All", "Instances", "Fediverse", etc, if you have any experience playing an MMO, there's an analogy that may help connect some of the dots;

• Lemmy Federation = MMO Server Regions (a cluster of servers connected to each other)
• Lemmy Instances = MMO Servers/Realms (a place where each account and its content is saved on the same physical hardware)
• Lemmy Community = MMO Guild (a group of individuals with similar interests)

Searching on "All" is akin to playing an MMO with cross-realm/server features enabled.

Sources:

• https://join-lemmy.org/docs/users/03-votes-and-ranking.html
• https://join-lemmy.org/docs/contributors/07-ranking-algo.html