Hi! In order to capture Group Summon such as Manda (Snake). Your Group needs to schedule a "Summon Capture" event. Once the event is scheduled, which can be done twice a week; the group can enter Summon Capture and battle the Summon. Battling the Summon will allow players to obtain rewards, which is dependent on the damage dealt to the Summon. The rewards would include the "Summon Fragments" such as the "Low-level summon fragment" which is needed to capture the Summon in order to use in Group Ninja War.

right now its says that manda is not open so what does that mean.

Ah! I thought you meant using the Group Capture feature in general =p The "Manda" summon itself is not released yet, which is why it is "Not Open". You will need to wait for it to be released first before being able to recruit it. Once there is more information in regards to the Manda summon, it will be announced/updated.