This depends on the role you have:
Step 1
Go to the map.
Step 2
Click on the select link
Step 3
Click on one of the direction links in the map to move.
Step 1
Move your army to a grid containing an enemy army.
Step 2
Go to the battlefield terrain.
Step 3
press on the battle button.
You must be a ninja or kunoichi to be able to assassinate rival players.
Step 1
Move your army to a grid containing a rival army, that is not allied.
Step 2
Go to the battlefield terrain.
Step 3
Find a player with a bounty placed on his head and press the assassinate button.
You must have a han and develop the settlements or farms in it.
Step 1
Go to the town that is the capital of the Han. This is often the nearest castle town.
Step 2
At the castle town you should see a free claim button somewhere at the bottom of the page. Lay claim to that town.
Go to the biography page of a rival player, to which your clan is not allied and press on the place bounty button.
Go to the trade and diplomacy section in the council and declare war on a rival clan.
If your clan is allied, then you must break the alliance.