Chain Hashing

Been following YouTube to study about Database Hash Join.
https://www.youtube.com/watch?v=J0nbgXIarhc
* HASH TABLE*
*Design Decision*
* #1: Hash Function *→ How to map a large key space into a smaller domain.
→ Trade-off between being fast vs. collision rate. Design Decision
*#2: Hashing Scheme* → How to handle key collisions after hashing. →
Trade-off between allocating a large hash table vs. additional instructions
to find/insert keys.

Now I have some idea about the Hash function, but the math part I have no
idea.
Hash Scheme is for handling collisions. Collision means that different
input keys will have some output hash bits.

The following part is about the *Chain Hashing. *

> Maintain a linked list of buckets for each slot in the hash table.
> Resolve collisions by placing all elements with the same hash key into the
> same bucket.
> → To determine whether an element is present, hash to its bucket and scan
> for it.
> → Insertions and deletions are generalizations of lookups.

I still don't get it. Stackoverflow seems don't have good answers yet.
So I come here, asking....