How are bloggers and professors so good at this? Is there a way I could practice on my own?
Instead, focus on saying simple and high-level things about the subject, and go into increasing levels of detail if you have more time, after checking that people are on board with you. For instance, you could start by saying 'blockchain is a form of internet money'. Great! What does that mean? They won't know, and this statement isn't even particularly accurate, but they will feel they understand you so far.
You could follow up with 'It is decentralized - that means it's not controlled by any government or bank. Instead, ordinary people all around the world work together to authorize transactions and release new money. There are many different kinds of blockchain. We often call the money that's released on a blockchain a cryptocurrency.'
Be very careful about dropping lots of jargon. Avoid using technical terms at all. (An exception for terms they've probably heard before like cryptocurrency or bitcoin miner - people like to tie together words they've heard before.) You want people to understand the high level concept, not the grandchild concepts. Be humble about the amount of knowledge you can convey in a short period of time. And be interesting! Be funny! Help people to stay attentive.
Also, you will get better at explaining any given concept if you practice it. Over time you will get faster, know what points tend to cause confusion and clear those up proactively, and ramble less. Make sure to talk with people instead of at them -- get their feedback. If they seem confused, see if you can figure out why, and work that into your talk!
Good luck.
IP -> post office + zip code domain names -> yellow pages