Create A Primary Key In Postgreg

Use SERIAL with PRIMARY KEY to create a unique primary key for a table. For example, here's the SQL to make a table with an id column as the primary key:

CREATE TABLE schema_name.table_name (
    id SERIAL PRIMARY KEY,
    another_column INT
);

Notes

Using SERIAL provides an auto incrementing number up to 2,147,483,647 that takes 4 bytes per row
There's also SMALLSERIAL and BIGSERIAL which go up to 32,767 with 2 bytes and 9,223,372,036,854,775,807 with 8 bytes, respectively

You don't need to bother with it unless you're interested in the details, but the different versions of SERIAL aren't really types. They're a "notational convenience". Check out the docs if you're interested in the specifics. Otherwise, you can just ignore it.
Another thing you probably won't have to mess with is an alternate method by making an IDENTITY column. You can't link to it directly but search for GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY [ ( sequence_options ) ] on this page for details that also tie into CREATE SEQUENCE

Note, if you try to create it with an integer, you'll get something like this as an error:

null value in column "id" of relation "example_table" violates not-null constraint

Create A Primary Key In Postgreg

Notes

Further Reading