There are three different resource types; Work, Material, and Cost.
Work Resources are people and machines, which need time (hours, days, weeks, etc.) to perform the Tasks.
Material Resources are consumables like bricks, wood, concrete, etc., they are independent of time.
Cost Resources are time independent resources, like Airplane tickets. If you are traveling from Oslo to Amsterdam it will cost you, approx. 300€, no matter how long will you travel (1 hour or 1,5 hours). If you are traveling from LA to Boston, the price will be different.
You can use cost resources to analyse how much you spent on insurance, travelling, etc.