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To add a bit to what the other posters have already noted, OSPF only supports equal cost load balancing. When you have multiple paths, end-to-end OSPF cost must be the same for multiple entries to appear in the route table.
On Cisco L3 devices, by default, Cisco computes OSPF cost by dividing 100 Mbps by what it believes interface bandwidth to be (can be adjusted by using bandwidth statement). OSPF cost can also be explicitly set on the interface.
Usually, Cisco routers will round-robin flows across the equal cost paths, i.e. at any one time different paths can show very different loads. (NB: PIRO version of PfR can dynamically load balance multiple flows.)
If one path equal path is lost, traffic will immediately use remaining path(s). (NB: immediately isn't actually zero time, but often very, very fast [faction of a second]. This is also after path is detected as being lost, which depending on topology and OSPF settings, can take a while [lots and lots of seconds].)
When multiple paths are available, usually a single flow will only use one path. Load balancing can also be done per packet, but generally not recommended.
