Is it secure?
Staking in Cardano means ADA never leaves your wallet. You always have control over your funds. When you delegate to a pool, you only give the Pool voting rights and the rights to earn more ADA on your behalf.
Choose a pool
There will be a section to delegate to a pool inside all of these wallets. Use the search bar and type the name of a pool ticker (eg HIMAL). Enter your ADA amount and confirm your selection.
Rewards are distributed to you every 5 days (known as an epoch) automatically by the protocol, after deducting pool fees. There is no way a pool can withhold or steal away your rewards. This is built right into Cardano and one of the reasons that makes it superior.
You are also free to use and send ADA from your wallet just like if you were not staking. So stake and chi!!