In order to restore to the most recent point in time (not only the the last full backup) we have to enable full recovery model.
In full recovery model the transaction log is not cyclic and the database will hang if there is no more room left in the transaction log. The only way to "clean" the transaction log is to backup it - results in *.trn files, the transaction log is usually backup every X hours to prevent it from runin out of space.
In order to be able to restore to the most recent point in time we need a full backup and every transaction log backup until current time.
Oded