My ipad has somehow locked itself while I used it. I dont know how to unlock it?

while I used my ipad somehow my ipad locked itself, and I am unable to go on the net. Up in the right hand corner appears a lock. I presume that this lock indicates that the ipad is locked. I dont know how to continue? I can open up my ipad with my code number, but not go on the net. how do I unlock it?