In order to start a Clan War in Clash of Clans you have to be a leader or one of the co-leaders in your Clan.
If you are a leader than you can start a Clan War by opening the Clan War screen and simply pressing the “Start War” button.
Please note that you have to have at least 10 members or more to start a war on Clash of Clans. If you don’t then you need to recruit some clan members.
Once you select the “Start War” button Clash of Clans will begin searching for a Clan that is in similar ranking as your own clan. They will look at both the strength of the clan and the number of members in both clans.
The Clan War will being when a suitable match is found between the two clans. It may take a few minutes for a match to be found; however, there is no need to wait in the match making screen.
Once Clash of Clans finds a match the game will automatically notify even if you are not playing the game at that time.
Good luck to all Clash of Clash clan members with their clan wars. We hope you guys win your battles.