Changing databases / schemas

Hi All

I have a question that might seem "blonde" but I am very new
to postgres and still trying to find my way around.

I need to work on a system which contains several databases
and schemas and the login I am using have access to all the databases and
schemas, etc...

However I am struggling to guide my way through the
databases,etc... to view the table structures and so on...

What I am trying to find out is the following:

. In MySQL for example you can use "use <database>" and then change
between databases which you want to access currently.

o Is there something similar in Postgres or do you need to disconnect and
reconnect to the next database everytime you want to change the current
working DB?

. Once connected to a database , how can I see a list of schemas and
in turn a list of tables that are currently available and also how do I see
the table info (i.e describe in other dbms systems)

I would appreciate any help in this as I tried to google but always seem to
just get results for Alter table, etc... (I think my search text might be a
bit off L )

Regards

Machiel