>Is it always necessary to do left and right join when you are joining a table? What is a better way to do this?

It depends on what you want to get with a particular SQL Select:

- Inner Join
returns only those rows that match on both sides.

- Outer Joins
Left Outer returns all rows of the left-side table, no matter if there is an equivalent on the right side regarding the On condition.
If there is no match, the right side will contain .Null. (unless you use NVL() in the field list).
Right Outer is the same vice-versa.
Full Outer Join returns all rows of both sides, with Null on the left side if there is no left-side match, and .Null. on the right side if there is no right-side match.

If you for example have a "customers" table and an "orders" table, then most likely all orders will have a match in the customers table, but not all customesr will have orders.
So you'd use an Outer Join to get all customers: customers is the left side, orders is the right side, a Left Outer makes sense:

Select * ;
From customers ; 
Left Join orders ;
    On orders.cust_id = customers.cust_id

hth
-Stefan