After the opening cutscene, you’ll have to set Byleth’s gender, name, date of birth, etc. Once done, you’ll meet up the young leaders of the Three Houses for the first time and you’ll be immediately thrown into your first battle.
If you’re familiar with the series, you should at least know the basics already like commanding units, moving, attacking, etc. Nevertheless, the game will provide tips since this is a tutorial battle anyway. Start off by taking out the lone bandit nearby.
Next, move your young allies towards Byleth and use the Talk command. Turn on the Danger Radius to see the enemies’ Attack Range then move your allies to the trees. Out of the four, keep Claude in the back row away from the enemies’ Range since he’s an Archer. Have your frontline units hide in the forest Terrain and lure the enemies into attacking them.
Continue clearing out the enemies nearby while taking advantage of the Terrain. Keep your units close and intercept the bandit leader’s forces coming from the northeast. Once you’ve met, Geralt will be able to reach the bandit leader as well because of his high movement Range. Finish off the bandit leader to trigger a cutscene.
You’ll be taken to Sothis’ realm in a brief instant. This will serve as a tutorial about the new mechanic of the game called Divine Pulse. Provide the correct answers to her to increase your Support. In any case, you don’t need to do any further actions at this point and the battle will end automatically.