I started working for a UK uni and they enrolled me into a pension scheme. They say they will contribute “5%”. 5 per cent of what? Is it my gross salary? My net? Also, will I get that if I opt out of the pension scheme? Is that 5% the only reason for being in a pension scheme? I’m sorry, I’m an immigrant an really do not understand why in the world would I give part of my money to someone who won’t give it back to me until I’m old. Why do people do it? Just for that 5%?
For UK workplace pensions you need to first read this: https://www.gov.uk/workplace-pensions
Employers are required by law to provide a pension scheme (and to auto enroll you with an opt out option). This is in addition to the state pension which comes out of your taxes.
The only reason to opt out would be if you plan to leave within the next 3 years or so and to not come back, otherwise you will need that money when you retire. If you are going down that route, you need to make sure that you invest the extra cash (i.e. your part of the pension contribution, you won't get the employer contribution) in whatever country you expect to retire to. Though, as someone who has private (as opposed to state) pensions in three countries, I still plan to get my money out of all of them when I retire, the extra money from the employer easily makes up for the administrative overhead.
University pensions in the UK are usually one of the better schemes (and unlikely to go bust), so opting out would be a mistake in all but the most specialist cases. If you do decide to do this, don't get your advice from random people off the Internet though.