Why do I need to stake my eos tokens ?


In eos you have to stake eos tokens in order to use the network resources (CPU and network bandwidth). If you plan to do a lot transactions or actions you will need a good amount staked, as actions consume the network resources, but these resources regenerate over time.
Besides, maintaining your eos staked is a good way to keep your eos tokens safe, as unstaking takes 3 days to complete.
When you stake, your eos are allocated between CPU and network bandwidth. CPU Bandwidth is your average CPU time consumption in microseconds over the last 3 days.  The longer your transaction runs, the more CPU bandwidth it will consume. Network Bandwidth is your average consumption in bytes over the last 3 days.