I hope you all are familiar with normalization if not please read it at least once.
First Normal Form:
Each set of a column must have unique value i.e. all relation in a domain must have atomic domains.
Let's try to understand this with the help of an example.
In this example, Rahul's Stream column must not contain two values then we have to separate in the different column because as per the rule of INF more than one value can't reside in the same column so we have to separate them.
We re-arrange the table as below, to convert it to First Normal Form (1 NF).
It's all about 1 NF, I hope you like it :)