In "Sid Meier's Civilization," controlling resources is one of the most important aspects of eventual world domination. While many resources, such as wood and iron, are plentiful and easy to harvest, others can be rarer, and more difficult. As a game progresses, uranium becomes one of the most coveted minerals, as it allows nations to build nuclear submarines, atomic bombs and the dreaded Giant Death Robot. Mining uranium presents a few problems, but is necessary for technological dominance.
Research both the Mine improvement option and the Atomic Theory technology, both of which are required before you can harvest uranium. Mine is an early and vital improvement that you will probably already have by the time uranium mining becomes a priority. Atomic Theory is a more expensive upgrade, and requires the Combustion technology. Once both have been researched, you can build a uranium mine.
Find a uranium tile and construct a mine. Once you've research Atomic Theory, any uranium deposits on the world map will become visible. You will need to construct a mine on one of these tiles to begin harvesting. Note that the uranium deposits are randomly generated on the map --- you may not have any within your territory. If that is the case, you will need to risk venturing out to claim unclaimed land, or to even steal territory from another player, to gain access to such deposits.
Begin harvesting uranium and apply it to your new technologies. Uranium is considered a strategic resource, meaning that it is in short supply on the map. Mines run out quickly, so harvest as much as you can, and use it wisely. If you have no pressing military conflicts, a nuclear plant is a great way to bolster a city's productivity, but requires one unit of uranium per day. Nuclear missiles are a powerful offensive weapon for those at war, and can destroy entire cities, killing every unit within two tiles of the detonation.
Civilisation has numerous ways for you to win over your opponents --- one is to acquire nuclear technology before the other players and surpass them quickly, either in terms of productivity or military might.