With the preferences dialog in the Configuration menue you can change some settings. GSms has two differnent ways for sending a SMS. The first and mostly used method is to send a http request to a webserver where you can send a sms. The other way is to send a email to your handy provider. It depends on the provider which method will be used.
If you want to send sms with email you must have an email account. For that you have to fill in the entries for sending and receiveing email. An option in the Receiving Mails section is delete messages from GSms. That means wheather GSms should delete the messages which are received for sending a SMS or not.
In the network section you can enter a proxy for sending http requests. The network timeout says how long should GSms wait when it gets no response from the other side until it closes the connection. The maximum number of threads while sending can also be changed.