Ore is a resource added in 1.0. It is obtained by mining. It is the only resource which is by default not loaded into the containers.
The level of Ore on a celestial body can be detected using a M700 Survey Scanner and for more detailed data in a particular biome a M4435 Narrow-Band Scanner can be used. Note that a polar orbit of 25000m* to 1,500,000m* is required to use the M700 scanner, this will of course vary a bit between objects but is a good estimate. To view the ore concentration on a planet right click the M700 Survey Scanner and select 'Toggle Overlay' and then you can use the Cutoff+ and Cutoff- to only show the highest concentrations to make it easier to decide the optimal mining location. To be able to view the ore data in the Tracking Station the scanned data need to be sent back using an antenna, and to watch the data you use the right panel of your screen where the Info and Orbit icons are there will be a new icon for Resources. Click the button and then select Resources -> Ore. A more precise determination for a particular location can be made using the Surface Scanning Module on a rover while landed.
Asteroids contain a finite amount of ore. If mining an asteroid, the mass of the asteroid will be reduced by the amount of ore extracted. There is no need to use any scanners to find out the ore concentration for asteroids, its enough to be close to it or own it.
Conversion into Other Resources
Ore can be converted into liquid fuel, oxidizer, and monopropellant using the ISRU Converter and electric charge. There is no change in total mass when converting to liquid fuel and/or oxidizer, but there is when converting to monopropellant. Conversion continues to function during time warp.