UI is the point when interactions between machines and people happen. It lays down the parameters of a user's interaction with a machine.
Candidate Block
In a few words, a candidate block is a block that a mining node (miner) is trying to mine in order to receive the block reward. So a candidate block may be described as a temporary block that will be either validated or discarded by the network. Miners compete with each other to validate the next block and add it to the blockchain, but first, they have to create a candidate block to participate in the mining competition.
Cryptocurrencies known as coins run on separate blockchains and are unrelated to other coins. Such a cryptocurrency's single unit is also known as a coin.