Basically you have to do 7 years in the company to get all of your contributions and the companies contributions back (and any profit of course). If you leave before that you dont get the companies contributions back (it varies a bit depending on when you leave)
Investing is up to you - there are about 10 approved funds of varying risk that you can invest all or part of your fund in. You can swap funds about 8 times a year without charge, otherwise it costs.
Contributions are compulsory.