Linked Servers are useful for server-to-server communication but if you're just needing to communicate from one database to another on the same instance then Linked Servers would not be a great option.

With the proper permissions any SQL statement executed within a database can use 3-part naming to access data in any other database on the instance, e.g. This

SELECT column_a

FROM dbA.dbo.table_a;

can be run in dbB to retrieve data.

SQL statements that use 3-part naming can belong to views, triggers, stored procedures, user-defined functions...pretty much any SQL object can contain a query with a 3-part name.