The connection involves two parts. First you connect to the ICQ server and then you login to the network using your UIN and password.
To connect to the server we use icq_Connect (line 220) and to log in we use icq_Login (line 229).
The arguments for the connect function are quite obvious (you need an address and a port number of an ICQ server). For the login function, you need the status you wish to login to. You can find the possible options for status in #define statements in lines 32-39.
so now we do:
icq_Connect(&link, ''icq.mirabilis.com'', 4000);