In few words:
You need 1 mil in inventory to join war. This war is different with war arena u was before, but first 10 minutes u will stay in lobby too. After 10 minutes, if you are not in waiting list (WL) u will be at battlefield. If you are in WL just wait and soon you will be in hopefully.
At battlefield you can press Tab to look map and V to look your score. You need to gain minimum 30 points.
Why 30 points? everyone who have 30+ points after war finished, will get:
1. WEXP
2. letter with buff capsule (u open it and get from it 300k, 500k or 5mil capsule, which u sell to NPC) and alz (you get alz only if your nation won, minimum u will get 950k alz. But the more points you have, more alz u will get)
3. AXP (after lvl 120)
How to get points? You gain your points when u attack procions/guards/towers or when u get damage from procions.