(a) Ahab married Jezebel, daughter of king of Sidon who brought her god (Baal) into Israel. Ahab worshipped it. Thus, Ahab provoked the anger of God more than all the kings of Israel before him. Elijah was sent by God to Ahab to denounce him and pronounce years of drought over Israel. Thereafter, God instructed Elijah to escape to the brook of Cherith where he could drink water and be fed by ravens. After a while, the brook dried up as there was no rain and God made for him an alternative arrangement as he escaped to Zarephath.
After three years of drought, Elijah was sent by God to confront Ahab and he challenged him to a contest at Mount Carmel to decide whom Israel must worship. At Mt. Carmel, Elijah ordered that two bulls be provided. Baal prophets were to choose one and prepare it for sacrifice to Baal while he too would prepare his own bull and whoever would get his sacrifices consumed by fire from his God would determine for all parties whom to serve. Baal prophets called upon their god all day to send down fire, but no fire came. Elijah taunted them to pray harder, but their god did not answer. When it came to his turn, Elijah ordered that water be poured lavishly on his own sacrifice. Despite all that, when he prayed, God answered with fire which consumed every thing, including the water. Baal prophets acknowledged Yahweh as God and Elijah ordered that all the false prophets be slain. Ahab was visibly shaken and was powerless to do any thing to harm Elijah. He rushed back home to report Elijah's victory to jezebel, his wife, who threatened to kill Elijah. God instructed Elijah to move to Horeb.

(b) Some lessons to be learnt about the nature of God from the episode are that:
(i) God's command must be obeyed, failure to do so means punishment.
(ii) God is above all kings/rulers and their subjects.
(iii) God controls nature, e.g. rain, drought, fire, etc.
(iv) He cares for those who obey Him, e.g. Elijah.
(v) God is a jealous God, He takes vengeance on anybody who raises his hand against His anointed children.
(vi) God's servants should be prepared for trials and persecution, but victory shall be theirs at the end.