You dont. Make a new file called start, then chmod +x start
Then you add this into the file with your favourite editor
#!/bin/bash
java -Xincgc -Xmx1536M -Xms100M -jar Tekkit.jar nogui
and then you just ./start when you saved your file.
If you want the server upp all time, type screen first then you ./start it.
ctrl+alt+d to get back to your normal screen and the server should be up until it crash or you reboot server
If you know what your doing you can use this http://forums.technicpack.net/index.php/topic,86.0.html to start/backup the server.