You will have a Net8 Easy config item from your start menu (I presume you want to connect from windows).

Run this, and in here you set up the alias.

All this means is that the alias is just a word which points to the database.

e.g.

alias = MYDB
--> TCP connection to 100.101.102.103, database name = TEST.

so when you connect in sqlplus for example, all you type in the three boxes is:
username
password
MYDB

The Net8 then uses the alias you supply to make the connection to the database called TEST on 101.102.103.104

Terry