You cannot apply online for them so set up an appointment with your closest SS office for inquiry and filing. You will need your own info, including your marriage certificate, as well as your late husband's info including his death certificate (see the publication)..
These Survivor benefits will be based on your late husband's record. Since he was evidently pretty young when he died, and if you file for these benefits BEFORE your full retirement age and thus as a reduced amount, the total received might not be that great. But the SSA can figure it and give you the amount.
If you do file for this benefit, be sure to ask them what, you should do when you reach YOUR full retirement age and have some earned benefits of your own - most likely there will be an adjustment upwards, if that be the case - meaning your own benefit is greater than the Survivor Benefit.. At that time, they will review it again.