First things first – any plots you have already completed and are farming cannot be added to a pool. You have to replot when/if you join a pool. Pools will be available later in the year, maybe June until then there is no safe way to join a pool. However,there are options to join unofficial pools that involve you giving away your private key, which is not recommended and means you are dependant on a third party. Pools are useful for smoothing out farming awards over time as you are likley to receive a small amount of chia regularly, as opposed to the very occassional larger reward (depending on network space).