Twitter does a few things I can't do with other platforms.
1. I can quickly search through all of someone's thoughts on a particular subjects, and all of people's thoughts on those thoughts, and peoples thoughts on those thoughts, etc.
2. I can comment on someone else's specific thought on a subject, and start a conversation thread on it.
3. I can subscribe to someone's thoughts, without them needing to write essays, etc. It provides a very low friction way to share thoughts.
4. I can build off of my previous thoughts, creating an interconnected web of all my thoughts on a topic. The link is not to a whole "essay" but to the individual thought from that essay that's relevant.
One way to think of twitter is a vast web of interconnected individual ideas. The character limit forces people to segment their tweets by thought, allowing for this to happen.
If you want to explore the community more, I recommend reading the Library, checking recent Curated posts, seeing if there are any meetups in your area, and checking out the Getting Started section of the LessWrong FAQ.
The Open Thread sequence is here.