See https://en.wikipedia.org/wiki/Cryptographic_hash_function#Properties
Quote
A cryptographic hash function must be able to withstand all known types of cryptanalytic attack. In theoretical cryptography, the security level of a cryptographic hash function has been defined using the following properties:
* Pre-image resistance
Given a hash value h it should be difficult to find any message m such that h = hash(m). This concept is related to that of one-way function. Functions that lack this property are vulnerable to preimage attacks.
* Second pre-image resistance
Given an input m1 it should be difficult to find different input m2 such that hash(m1) = hash(m2). Functions that lack this property are vulnerable to second-preimage attacks.
* Collision resistance
It should be difficult to find two different messages m1 and m2 such that hash(m1) = hash(m2). Such a pair is called a cryptographic hash collision. This property is sometimes referred to as strong collision resistance. It requires a hash value at least twice as long as that required for preimage-resistance; otherwise collisions may be found by a birthday attack.[2]
* Pre-image resistance
Given a hash value h it should be difficult to find any message m such that h = hash(m). This concept is related to that of one-way function. Functions that lack this property are vulnerable to preimage attacks.
* Second pre-image resistance
Given an input m1 it should be difficult to find different input m2 such that hash(m1) = hash(m2). Functions that lack this property are vulnerable to second-preimage attacks.
* Collision resistance
It should be difficult to find two different messages m1 and m2 such that hash(m1) = hash(m2). Such a pair is called a cryptographic hash collision. This property is sometimes referred to as strong collision resistance. It requires a hash value at least twice as long as that required for preimage-resistance; otherwise collisions may be found by a birthday attack.[2]
For understanding how hash values and preimages are actually used to build payment channels, I think this series of articles from bitcoinmagazine are pretty good: https://bitcoinmagazine.com/articles/understanding-the-lightning-network-part-building-a-bidirectional-payment-channel-1464710791/ Hopefully it answers your question.