Worshipper – “Ship” [Campaign 2, Mission 4]

It’s best not to delay in this mission; you need to use a blitzkrieg tactic. First, capture the first city of the Forest Alliance, then Inferno, and continue through the Dungeon until you reach the surface. You can follow the main path, or you can turn into one of the branches of the Dungeon (it seems to be the second one), and after just one day's travel, there will be an elven garrison there. Capturing it will allow you to take the second city of the Forest Alliance much faster. The third city will be at the opposite end of the map, but it is unlikely to offer significant resistance, so you don't need to rush to it.
Also, in the city of Inferno, in order to preserve your elf army (since you cannot quickly gather many troops in Inferno, it is better to leave the elves behind), I recommend hiring a secondary hero who should follow Agrael and collect his troops at the end of each turn. This way, soldiers won't desert from the army.
And along the way, of course, you need to capture mines, dwellings, etc..
Have fun playing! :)
P.S. When I recently completed this mission, several squads of archers joined me for some reason at the very beginning. Because of this, I didn’t use the Inferno army throughout almost the entire mission. Perhaps you will be as lucky, and you will easily eliminate any opponent in your path.

Please describe how to complete the entire campaign in more detail. Thank you in advance.

Look for tips in the relevant topics of this section on completing the game. For example, in this one.