Two novice questions

I have received a collection of scripts to be used to build a PostgreSQL
db and I can't figure out the following.

1.  Usage of quotes in the scripts.
The following comes from a script to build and populate a table:
gid serial PRIMARY KEY,
"fid_" int4,
Why is the second column name in quotes, i.e. what is the difference
between fid_ int4 and "fid_" int 4.

In a similar vein, this comes from a  script that creates a couple of
tables:
create table schema1."cache" ( ...
create table schema1.cache2 ( ...
Here one schema name is quoted and the other is not.

2.  How does one run a script from PGAdmin?  I have been 'opening' the
script file then hitting the run button.  Is there a way to just specify
the path to the script?

Thanks for any help or pointers,
-=beeky