Staking NEAR
Go to the Staking tab;
Click "Stake my tokens";
Choose your validator. There are many considerations to choosing a validator, some of which include the cost of delegation (a percentage of your rewards), the reliability of the validator (check https://near-staking.com to learn more), and the current total stake size;
Click "Stake With Validator";
Enter the amount to stake;
Click "Submit Stake" and authorize the transactions. You may need to authorize several transactions if you are staking from a lockup.
Unstaking NEAR
Note: Unstaking will take up to 72 hours, and your NEAR will be completely locked during this time. Unstaking again before your NEAR has finished unstaking will reset the clock.
Go to the Staking tab;
Scroll down and find the validator you would like to unstake from in "Current Validators";
Click the validator's name;
Click the "Unstake" button;
Enter the amount to unstake;
Click "Unstake Tokens" and authorize the transactions.
Withdrawing
Go to the Staking tab;
Scroll down and find the validator you would like to unstake from in "Current Validators";
Click the validator's name;
Click the "Withdraw" button and authorize the transactions.