The system connects the wallet itself to the baker (validator), and rewards are automatically distributed based on the tokens held in the wallet. The entire quantity held in the wallet will continue to be staked (but no reward will be given until the minimum amount of 1 XTZ is held). For this reason, there is no ability to staking only some tokens. Also, you can freely send and receive tokens in your wallet at any time, even while connected to Baker. There is no lock period.
Rewards will start to be distributed 7 rounds after you connect to the baker, and will be distributed every round after that. 1 round takes approximately 3 days, so you will not receive any rewards for a while after connecting to the baker. The rewards are automatically distributed from the blockchain, so there is no action to "accept" the rewards.
You can send and receive tokens freely while staking. Since there are no restrictions, you cannot (and do not have to) unlock staking. Since there is no unlocking, there is no lock period.