We have been trying to access new company with the admin login but showing an error like "Incorrect Password" other than default company. Please guide us in detail. Thank you in advance.

If you fail to provide a password during company creation, then the default is "password" for the "admin" user. Only the default company login can create a new company. You need to login into the new company with your access credentials by choosing the right company in the login's dropdown select box (or textbox if set in config.php).

Actually I am new on it, kindly provide me step by step instructions to create multiple company.

The first company which I created I haven't given any table prefix is it so that If I want to create multiple companies I have to add table prefix because I created new company with new database but still it gives me error wrong password or username