If you need to accomplish maintenance tasks on your Derbi Terra 125 then it is usually a good plan to have a Workshop Manual to keep just for personal reference in the event that you need to know how you can take out a specific component for example the Exhaust and install it again in the correct manner.
Derbi Terra 125 Workshop Manuals gives you targeted diagnostic facts for your car therefore if something is wrong it will help you figure out what the problem is and methods to correct it. After that you can analyse if you can do this on your own or in the event the job is too big you can actually book your Terra 125 right into a nearby car garage.
Derbi Terra 125 manual