It's all written in
DEPLOYMENT PROCEDURE paragraph inside
ScenarioX Army List usage Article.
I'll sum it up here:
Deployment Procedure
1. Both players roll a die and add the score to their army’s initiative factor. If initiative is tied then no terrain is deployed, and the players should dice to decide who will be the attacker/ defender for purposes of troop deployment - go to step 4 and continue (skip steps 2 and 3). Otherwise, the side with the higher total initiative is the attacker and the other side the defender for all purposes - go to step 2 and continue.
2. Each army has a home terrain type. According to their home terrain type the defender now places compulsory terrain, plus as many of the optional terrain hexes as they wish, anywhere on the board – see ‘Placing Terrain’ below. Note that rivers must start at the board edge. They may be any length and may stop anywhere. They are fordable along their entire length.
(if you use a predefined setup you could ignore terrain deployment).
3. Roll a die. The attacker gets to choose which long side to set up on with a roll of green, blue, or red. On any other roll the defender chooses.
4. The defender now deploys their troops within two hexes of their base edge, placing a second general with any one of their units (optionally, the second general may be deployed after the drawing of command cards). Light troops and leaders may deploy within three hexes of the base edge. Additionally, if a town hex is on the board the defender may deploy any infantry unit from their army in that hex regardless of where the town is.
5. The attacker then sets up on the opposite board edge following the rules in step 4, but may not deploy infantry into vacant town hexes beyond their deployment area.
6. The defender may now redeploy any two units to anywhere within two hexes (three hexes for light troops) of their own base edge. For this purpose a leader counts as a unit.
7. Both sides receive 5 cards. The attacker draws first.
8. Victory is 6 banners, and the attacker begins.
P.S. I've also added a link in the TOP of Randomizer PAge, for easy reference.