The Bridge (Sirat) is the bridge that is extended over Hellfire to which the people come and cross with speeds and ease proportional to their deeds. One end of the bridge is on the changed earth and the other end is after Hellfire towards Paradise.
At that time, some of the believers do not step on the Bridge, but rather they will fly over it. Other believers will walk on it. Those who walk of the Bridge are of two types; some will fall into Hellfire, and the rest will be saved. On the other hand, all the blasphemers will fall into it. Allah ta^ala said in Surat Maryam verse #71:
﴿وإن منكم إلا واردها﴾ سورة مريم
The verse means: [There is not one of you but shall approach it.]