Primary Key: -

1. The Primary key is used to identify rows or data uniquely from the table hence table cannot have duplicate data.
2. A table can have only one primary key.
3. Automatically apply Cluster index to the column which has a primary key.
4. It is not accepting null values.

Foreign Key :

1. A table Primary key becomes a Foreign key in another table. It helps to maintain the relationship between two or more tables.
2. A table can have multiple Foreign keys.
3. Not apply cluster index.
4. Accept null value

eg.
For example, We have two tables student and Course.

Student table has STUID which is primary key of Student Table and Foreign key in COURSE table.

STUDENT TABLE

COURSE TABLE

A primary key is used to ensure data in the specific column is unique. It is a column cannot have NULL values.
Where as a foreign key is a column or group of columns in a relational database table that provides a link between data in two tables.
See this below link for full difference,

https://www.guru99.com/difference-between-primary-key-and-foreign-key.html

I can think of below three points:

1. Primary key is used to uniquely identify a row.Foreign key is used to connect two tables or maintain relationship between them
2. Primary key can not have null values. Foreign key can have multiple null values
3. Primary key can not be deleted from table unless all the references are deleted from other tables . Foreign key can be deleted

Reference: Scaler Topics