We need a bit more context. But i will try help !
For example if a group of people all wrote a statement on a piece of paper about a particular event. And you then picked up one of the pieces of paper and asked one of the people directly 'is this your statement?' and the person responded yes then you could say 'are you sure?' and if they replied yes again, you would say 'ok !! i believe you'
You would use the verb 'to accept' when you are accepting a challenge,invitation to a certain place etc.