To connect to SQl server select "Connect ..." from the File menu or click coresponding button on the toolbar.
Assuming SybSQL is able to locate interfaces file , you will be presented with the Login dialog where you can select SQL server from the list of available servers.
If SybSQL is unable to find interfaces file, you will be offered option to create temporary one valid for the duration of the program execution.

When connection to the server is requested, SybSQL looks for enviromental variable named SYBASE which should point to the directory where interfaces file is located. If there is no such variable, it tries to find this file in /opt/sybase and if this fails, the program will give up and ask you for assistance.
If you planning to use this program frequently it would be advisable to create SYBASE variable pointing to the directory containing interfaces file
Below is simple .bash_profile file with SYBASE variable set to /opt/sybase. ( .bash_profile is located in your home directory.)

# .bash_profile

# Get the aliases and functions
if [ -f ~/.bashrc ]; then
        . ~/.bashrc
fi

# User specific environment and startup programs


QTDIR=/usr/local/qt2
PATH=$PATH:$HOME/bin:$QTDIR/bin:/usr/local/bin:/opt/kde/bin:
KDEDIR=/opt/kde
ENV=$HOME/.bashrc
USERNAME="warmi"
MANPATH=/usr/man:/usr/local/man:/usr/X11R6/man:/usr/lib/perl5/man:/usr/local/qt2/man
CPLUS_INCLUDE_PATH=$QTDIR/include:$CPLUS_INCLUDE_PATH
EDITOR=pico
TMAKEPATH=/usr/local/lib/linux-g++
SYBASE=/opt/sybase
XBMLANGPATH=/tmp
export USERNAME ENV PATH KDEDIR  QTDIR CPLUS_INCLUDE_PATH MANPATH EDITOR TMAKEPATH SYBASE XBMLANGPATH