Auto Liability for trucking works the same way as for your personal auto. It covers (based on the policy) property damage and bodily injury to others. This is a required coverage by the DOT when owning a trucking company. Unlike your personal auto, the liability limits will be higher. The liability limits range from $100K to $1M in most cases your brokers and contracts will require the $1M.
If you are running a trucking operation where the GVW is over 10K you will just want to look at higher limits, than the $100K. Yes, the premium is higher, but less hassles for you when trying to get loads. Some insurance companies will have their own minimum limits for you to be with them. If you have an MC-90, the minimum limit is $750K to be compliant with the FMCSA.
Check with our brokers and contracts for their required limits before shopping for your insurance so you don't have to go through raising them if you do not meet their requirements.