Starting GATE:

You must be connected to the internet when you start GATE, or GATE will be unable to load the xml-schemas that specifiy the MPQA annotation types. However, you do not need to remain connected to the internet as you continue to work in GATE.

Windows: Double click on the gate shortcut on your desktop or find it via Start->All Programs->GATE-3.1 (or similar).

UNIX: The hard-core way is to cd inside the GATE installation directory and then type "bin/ant run". You may be able to do this more easily, say with a desktop icon, depending on the linux version and your knowledge of linux.