The size of wingfoil you should use as a beginner depends on a few factors, including your weight, ability level, and the conditions you will be wingfoiling in. Here are some general guidelines to help you choose the right size wingfoil for you:

If you are a very light weight rider (less than 70 kg / 154 lbs), you may want to start with a smaller wingfoil, such as a 3.5 or 4.0 meter wing.

If you are a medium weight rider (70-80 kg / 154-176 lbs), you may want to start with a medium size wingfoil, such as a 4.5 or 5.0 meter wing.

If you are a heavy weight rider (over 80 kg / 176 lbs), you may want to start with a larger wingfoil, such as a 5.5 or 6.0 meter wing.

It's important to note that these are just general guidelines and you may need to adjust based on your specific circumstances. For example, if you are a heavier rider but the conditions are very windy, you may want to start with a smaller wingfoil to make it easier to control. 

It's always a good idea to speak with a local wingfoil instructor or shop to get personalized recommendations for your specific situation.