Basically you just click a button in the wallet and enter the address of the leasing pool. As for returns you are best off asking that in bitcointalk or Slack as I haven't been monitoring the returns that closely - seems quite small right now but then I only recently put a decent amount of Waves in the wallet. There are also the Waves community tokens which get paid out according to your stake every month and entitle you to a certain proportion of ICO tokens.