You dilute the concentrate to the recommended level (10:1) and immerse the item to be de-rusted. Immersion time depends on level of rusting but normally takes between 3 and 10 days. It is hard to 'over-IReOx' so leave as long as necessary.
IReOx does not affect rubber so suspension bushes can be left in place. It also doesn't attack paint (please test an area first) so we have used it to strip rusted drop link threads without affecting the painted suspension arm.
Larger sizes are available in the IREoX section but this 1 litre is usually plenty for this application. It makes around 10 litres of solution.
IReOx is based on natural molasses, a by product of sugar cane processing. It is therefore natural, harmless to humans and kind on the environment - yet more potent on rust than anything else you can safely use at home. It can be handled without special safety equipment but it does pong a bit, so gloves are recommended.