How do you get swings to be stable/safe?

[Mercedes]

We've been given a metal swing for my dd. I can how you assemble it and it seems to have spikes that fit in the poles that stick in the grass. Is this enough?
The person who gave us the swing muttered something about bricks or concrete to hold it down?
Has anyone done this and could give us advice so we don't make a mess of it?

CEMENT SORRY THOUGH NO IDEA WHAT YOUHAVE TO DO GRANDAD DID OURS LOL

My Dad set the four 'legs' of our swing in concrete and it has been fine (4 years and still going strong).