What is Tangle ledger technology?
Tangle ledger is the unique technology, based on a directed acyclic graph (DAG). DAG is mathematic-computer science theory, that graph consists unlimited vertices and edge connected to each other. (For more detail see Wikipedia definition). So, the main technology is absolutely opposite to the classic blockchain technology. Tangle technology is main the technology of IOTA project.
It’s very hard to understand, how exactly Tangle works because there are a lot of technical terms. If you want completely know, how tangle works, you can look on Tangle blog. Also, you look at Tangle whitepaper.