The infinitive and the present participle of all verbs are formed in the same way.
Traditionally the present infinitive is the basic form of the verb. It is composed of the present stem and the infinitive ending en.
The present participle is formed with the present stem and the ending end. Since the final d is the only difference between the endings of the participle and the infinitive, one can also say that the participle is formed by adding d to the infinitive: