You need to execute a query either manually or you can use other tools as for example PLSQL Developer can execute a query by using the development tool.
Below SQL query can be used by PLSQL Developer:
select table_name, constraint_name, status, owner
where r_owner = :r_owner
and constraint_type = 'R'
and r_constraint_name in
select constraint_name from all_constraints
where constraint_type in ('P', 'U')
and table_name = :r_table_name
and owner = :r_owner
order by table_name, constraint_name
In the above query r_owner is the schema, and r_table_name is the table for which we are looking for references.
Note: Here, all the names are case sensitive.
But, Oracle SQL Developers don't have the option to find which table reference a given table is having.