psql syntax errors when trying to run sql script to create a table

I was provided a .sql script containing a query to create a table. I trust the source of the script, so I am wondering if the problem is how/where I'm running it. I'm running it in psql, using a call like \i c:/Users/.../sql_script.sql. Here is the code in the script, modified slightly to make it look generic:

CREATE TABLE dbo.mytable (
	id int NOT NULL IDENTITY(1,1),
	userID int NULL,
	Probability DECIMAL(18,8) NULL,
	Conv_Thresh1 int NULL,
	Conv_Thresh2 int NULL,
	DateAddedToDB date NULL
);

ALTER TABLE dbo.mytable ADD CONSTRAINT some_text_i_dont_understand PRIMARY KEY (id);

CREATE NONCLUSTERED INDEX i1 ON mytable  (userID);

And here are the errors I'm seeing:

.sql:8: ERROR:  syntax error at or near "IDENTITY"
LINE 2:  id int NOT NULL IDENTITY(1,1),
                         ^
ALTER TABLE

and

.sql:12: ERROR:  syntax error at or near "NONCLUSTERED"
LINE 1: CREATE NONCLUSTERED INDEX i1 ON mytable  ...

Is this a problem with the script itself? I see similar errors trying to run other "table creation query" sql scripts that have been provided to me, so I'm wondering if it's more about me not understanding psql/postgres. Thank you

Q: Is this a problem with the script itself?

In a way, yes. This script is apparently meant for Microsoft SQL Server, whose syntax and features differ from PostgreSQL in many aspects.

The syntax looks for MSSQL Server. For postgres it would have been like:

CREATE TABLE mytable (
    id INT GENERATED ALWAYS AS IDENTITY
);

More info on using identity with postgres.