I've done my fair share of woodworking and carpentry that I've used oils to both treat/finish wood and to maintain tools and am familiar with the hazards of not disposing it off properly.
As for using boiled linseed oil which dries quickly (actual linseed oil can take ages) to maintain your tools, just dip a rag (cotton wool or a cloth) in them and coat a thin layer of oil on the metallic parts. Make sure to cover evenly and leave no spot untouched. This will provide a layer of protection against rust formation. The principle behind this is very simple - by coating with a thin layer of oil, you're cutting off oxygen supply, hence preventing the iron from oxidizing and rusting.
However, do not be tempted to add multiple coats or a thick layer of oil. Thicker layers take longer to dry and often, do not dry to form a hard surface (i.e., it requires exposure to air to dry and thick coats will remain soft underneath the surface). This can be quite deceptive, meaning it gives an appearance of having dried, but really it hasn't. Multiple layers of thin coats are also not a good idea, because they become prone to being removed when scratched i.e., the layers will peel off more easily when thick than when thin.
You may start using the tool once it has dried (you can try gently running your fingers on it. If your fingers don't have an oily smudge or very little of it, it has dried). You do not have to coat it after every use. It would be better for the tool if you had a maintenance schedule. However, if your use is very sporadic (i.e., use today then 3 months later), then it would be worth your while to coat it each time.
The rags you use should never be disposed as is. The are combustible and could result in fire damage. Treat this as a general advice for any rags containing mineral oils/paint thinners/acetone/etc and for wood dust/wood shavings from previously finished wood. Piling them on will cause an exothermic reaction (heat releasing) and eventually result in spontaneous combustion. You can wash them under running water several times until it's "free" of it, while at the same time collecting the water + oil mix in a bucket. Later, take the "hazardous waste" to your local collection center. If they charge you by volume, then instead of running water, you can wash it in still water (however, I'm not a big fan of this, as it only leads to more messiness).