The block height is the number of blocks that came before the chain’s genesis block (first block).
For example, Height 0 would be the genesis block. If a new block were mined and added to the blockchain, it would have a height of 1.
It’s important to note that “height” does not mean “confirmations” for a transaction. Someone can mine a new block that contains a transaction sent by you, and if someone else were to mine another block on top of that one, your transaction in that second block would have two confirmations.
The height of the block containing your transaction only indicates how far back the block is from the genesis block.
For example, if we had just 10 miners, each hashing at 10 hashes per second, it would take around 100 seconds until someone found a new block (10×10 = 100). But what if we increase the number of miners? Then it will take less time for someone to find a new block. If we had 20 miners hashing at 10 hashes per second, it would only take 50 seconds until someone found a new block (20×10 = 200; 200/2 = 100).