Today, when I drove my car, the clutch suddenly has no tension and I couldn't go in any gear. So, I stopped the car at the side. When I pressed the the clutch, it didn't go back to the normal position. The main thing is I found some oil leaking under the center of car. Do you guys know any problem for my car??

 

What problem to your car be probably bad clutch slave cylinder. Get under your car and find the source of that leak.

 

that could be a clutch fork too.