A good way to find gerund is looking for -ing connected to the verb, putting -ing after is how the gerund is formed! :)

You are asking whether the object of a verb should be a gerund or an infinitive. There is no really good rule. A few verbs, such as like or love, can take either. Phrasal verbs take a gerund, but otherwise a person must memorize on a case-by-case basis. I am sorry not to be more help.