suppose you have two databases: db1 and db2
you have to select one of them
as
sql>use db1;
then use
sql>select * from tab;
it will show you the listing required.!

Suppose your 2 databases are name as PROD1 and PROD2
1) How can create a table in particular database?
=> First you have to connect to the database where you want 
to create table with given login and password.
and then if you have create permission than you can use 
following sql
CREATE TABLE "table_name"
("column 1" "data_type_for_column_1",
"column 2" "data_type_for_column_2",
... )

2) select * from tab; will show you how many tables,view or 
synonyms are there in your schema.

you can also use the database links to get the data from 
other database tables. syntax is table_name@db_link.