First you make sure you connect to your distributor server with [server\instance]
from you publisher server.
Also you need to set up all the replication accounts and make sure they have the right permissions
and you need to create the distribution database in your distributor_server
there is this script as an example:
-- This script uses sqlcmd scripting variables. They are in the form
-- $(MyVariable). For information about how to use scripting variables
-- on the command line and in SQL Server Management Studio, see the
-- "Executing Replication Scripts" section in the topic
-- "Programming Replication Using System Stored Procedures".
-- Install the Distributor and the distribution database.
DECLARE @distributor AS sysname;
DECLARE @distributionDB AS sysname;
DECLARE @publisher AS sysname;
DECLARE @directory AS nvarchar(500);
DECLARE @publicationDB AS sysname;
-- Specify the Distributor name.
SET @distributor = $(DistPubServer);
-- Specify the distribution database.
SET @distributionDB = N'distribution';
-- Specify the Publisher name.
SET @publisher = $(DistPubServer);
-- Specify the replication working directory.
SET @directory = N'\' + $(DistPubServer) + '\repldata';
-- Specify the publication database.
SET @publicationDB = N'AdventureWorks2012';
-- Install the server MYDISTPUB as a Distributor using the defaults,
-- including autogenerating the distributor password.
USE master
EXEC sp_adddistributor @distributor = @distributor;
-- Create a new distribution database using the defaults, including
-- using Windows Authentication.
USE master
EXEC sp_adddistributiondb @database = @distributionDB,
@security_mode = 1;
GO
-- Create a Publisher and enable AdventureWorks2012 for replication.
-- Add MYDISTPUB as a publisher with MYDISTPUB as a local distributor
-- and use Windows Authentication.
DECLARE @distributionDB AS sysname;
DECLARE @publisher AS sysname;
-- Specify the distribution database.
SET @distributionDB = N'distribution';
-- Specify the Publisher name.
SET @publisher = $(DistPubServer);
USE [distribution]
EXEC sp_adddistpublisher @publisher=@publisher,
@distribution_db=@distributionDB,
@security_mode = 1;
GO
You can also have a look at the way I got it done: call the procedure sp_adddistpublisher as shown here.