Gerunds

A gerund is a "verbal noun." Formed from the verb stem, it's used as a noun. It's somewhat similar to English verb forms ending in -ing (though that form is used as a present participle too). So, there isn't a good map between Latin and English:

Marcus ambulat.              (present indicative)   Mark is walking.
Ambulare est facile.         (infinitive)           Walking is easy.
Uluantem lupum effugi.       (present participle)   I fled the wolf who was howling.
Bene sciuit artem coquendi.  (gerund)               He new well the art of cooking.

The gerund is formed using the verb's stem plus nd + case endings. However, gerunds are neuter, never plural (despite apparent subject) and never nominative.

Samples

genitive    Spes vincendi.             He had hopes of winning.
ablative    ...gratia/causa vicendi.   because/for the sake of winning.
dative      Laudando persuadebat.      He was persuade by praising.
accusative  ...ad vincendum.           for the purpose of winning.