How do you create a variable load on something like a wind turbine?
First you need something that you can dump power into. Useful sinks are a battery bank that can accept charge, or a grid tie inverter to push power into the grid. If you simply want to brake the turbine, then a bank of heaters will dump power, but you don't get anything back! Of course a battery bank can get fully charged, and then you may want to dump power into heaters anyway.

Then you put an inverter between the turbine and the load (or the battery charger or grid tie inverter is programmable), program the inverter output so that it will deliver X amount of power to the load. The MPPT algorithm adjusts the programming so that X is maximised.

If you simply want to brake the turbine, MPPT may not be appropriate, and you'd alter the inverter programming until the turbine speed was what you wanted.