Debugging question ...

Hi All,
I've been using MS SQL 2k and it's bundled query analyzer SQL editor for
more than 5 years. I am exploring postgres right now and I hit a snag I
don't understand...

MS SQL : debugging - use query analyzer, declare variables, plug in code
and test...

PG : using PGAdminIII editor :

declare

tst int; (or whatever variable)

there is an error already....syntax error...

I did some research and it seems that variables cannot be declared
outside a function scope? Looking at functions within PG, the
implementation looks like one massive dynamic sql string....

I wanted to figure out how PG handles single quotes, double quotes,
string concats and such.... problem is that the editor won't even let me
declare variables...ahmm help? how does one debug in PG? what tool?
anything like query analyzer of MS SQL? why can't I declare variables
and print the values out to check and debug? HELP? Many Thanks in
advance...