Learn Arabic (Modern Standard): أنا نسيت موعد الاجتماع.

In Arabic past tense verbs, the person who did the action is shown by a suffix (an ending) attached to the verb. The ending ـتُ (-tu) specifically means "I". Because the verb itself already includes "I", the separate pronoun أنا (ana) isn't strictly necessary, but it is often used for emphasis.

What is the base form of the verb نسيت?

When looking up an Arabic verb, the base or dictionary form is always the "he" past tense version. For this verb, it is نَسِيَ (nasiya), meaning "he forgot". To make it "I forgot", you replace the final short vowel with the "I" suffix ـتُ (-tu) to make نسيتُ (nasiytu).

Why is there no Arabic word for "of" in "the time of the meeting"?

Arabic uses a special pairing of nouns called an Idafa to express "of" or possession. You simply place the two nouns right next to each other. The first noun, موعد (time/appointment), is not allowed to have "the" (الـ) attached to it. The second noun, الاجتماع (the meeting), usually does. Placed together as موعد الاجتماع, it automatically means "the time of the meeting".

Does موعد just mean "time"?

It specifically means a "scheduled time", "appointment", or "date". If you are talking about time in a general sense, like saying "I don't have enough time" or asking "what time is it?", you would use a different word: وقت (waqt).