Ores are blocks that exist in veins around the world which can be extracted and then smelted into bars. Once found, each ore can be scanned at the research station for some research points.
Once an ore is researched, using the Ore Scanner on a vein will tell you the amount of ore it contains. Without upgrades, each ore mined from a vein using an Ore Extractor subtracts 10 total ore from the vein. Therefore, using an ore extractor without upgraded drill heads will subtract 40 ore from the vein every 30 seconds.
Each vein has it's own volume. Basically, every 1m3 of ore vein contains 180-2560 ores. You can see vein volume and ore amount after scanning it.
Note: Tier 1 and 2 ores can only stack in your inventory up to 150 per slot, therefore it is highly recommended you automate ore directly to smelters as bars can stack indefinitely.