Help with installing mail server


Hello i have instaled ubuntu server and i want to create own mail server, i have made everithing which was in this manual , but i have some question, i have configure postfix dovecot mysql and i have installed vimbadmin. Now i want install roundcube but i have problem with the instalation.

My first question is how can i install roundcube only in terminal ? My second question is, when i will have roundcube how can i configure it that will work with vimbadmin? I will create a domain for example in vimbadmin and how can i configure roundcube that this mail adress will work ? My third question is when i install roundcube what is the first login username and password ?

Please im new in installing mail server and i hope that somebody will me help