Spanish/Tenses/Gerund

Some things to note:
 * 1) Verbs that are -Er/-Ir double vowel verbs (caer, creer, leer, huir, etc.) will substitute a 'y' for the 'i' in the ending: cayendo, creyendo, leyendo, huyendo, etc.  This does not include -guir verbs, as the 'u' exists only to elecit the hard 'g' sound and is not pronounced.  This same change occurs in the third person of the preterit.
 * 2) With -Ir stem changing verbs (morir, dormir, sentir, vestir, pedir) the 'o' in the stem will change to a 'u' (muriendo, durmiendo), or the 'e' to an 'i' (sintiendo, vistiendo, pidiendo). This same change occurs in the third person of the preterit and the nosotros and vosotros of the present subjunctive.
 * 3) Ir has the irregular gerund, yendo, and poder the irregular gerund pudiendo.
 * 4) These are not nouns. Me gusta nadando is incorrect. While in English, we say "I like swimming," you cannot do so in Spanish. "Swimming" can be either a verb or noun in English, meaning "moving through water" (a verb) or the act of doing so (a noun). In Spanish, you say "me gusta nadar". "I like to swim."
 * 5) These forms are often used with the verb estar, for use in continuous tenses. When used as such, it is estar that is conjugated to agree with the subject. The gerund does not change. Ellas están hablando is correct, while ellas están hablandas is not.
 * 6) -ER and -IR verbs undergo the same change to make the gerund.