Start by laying baby on the poolside with feet at the edge and head away.

Sit on the side next to your baby, place one hand on one side of baby and whilst maintaining eye contact place the other hand on the other side of baby and slowly lower yourself into the water.

Once your feet are firmly on the ground you can then start to bring your baby into the pool. 

If baby is sitting up and you know they can sit without assistance you can sit baby on the poolside, just ensure they are far enough away from the pool edge so that they wont fall into the pool.