At the beginning of combat on your turn, up to one target land you control becomes an X/X green and blue Bird creature with flying and haste until end of turn, where X is the number of cards in your hand. It's still a land.
Whenever a land creature you control deals combat damage to a player, draw a card.
Jolrael's last ability applies to any land creature you control that deals combat damage to a player, not only lands that become land creatures because of Jolrael's first ability.
12 May 2023
Use the number of cards in your hand as Jolrael's first ability resolves to determine the value of X. Once the ability resolves, that value is locked in. The power and toughness of the land creature won't change if the number of cards in your hand changes later in the turn.