How to show relationship between columns of 2 tables

1. Can 2 tables have 2 relationships?
2. Which key shows relationship between two tables?

Can 2 tables have 2 relationships?

Yes, it is allowed. You can have as many FKs as you like. btw: It is a 1:N relationship, not 1:1.

Which key shows relationship between two tables?

A foreign key helps to define the relationship among tables . This unique key communicates one or more interrelationships in a relational database between two or more tables.