Tarkkailen pilviä parvekkeelta.

Tarkkailen is the first‐person singular present form of the verb tarkkailla, which means “to observe” or “to watch carefully.”
• The infinitive is tarkkailla (“to observe”).
• In the present tense, type I verbs like this add -en for “I,” so tarkkailla → tarkkailen (“I observe/watch”).

Finnish uses the partitive case for:
1) Ongoing, incomplete, or unbounded actions (aspect).
2) Direct objects of many verbs when the object isn’t a single, whole entity.
Here, “observing clouds” is an ongoing activity, and pilviä (“clouds” in partitive plural) correctly signals that you’re watching some clouds, not counting or completing them.

• Katsoa means “to look” or “to watch” in a general sense (like “watch TV”).
• Tarkkailla implies more careful, prolonged observation—“to observe,” “to monitor” or “to keep an eye on.”
In this sentence, you’re not just glancing at clouds; you’re observing their shapes/movements in detail.

Parvekkeelta is the ablative case (adessive -lla/llä + suffix -ta/ltä → -lta/ltä), indicating “from” somewhere.
• Parveke = balcony
• Parvekkeella = on the balcony (adessive “at/on”)
• Parvekkeelta = from the balcony (ablative “from”)

Yes, but with a nuance change:
• Parvekkeella (“on the balcony”) states your location while observing.
• Parvekkeelta (“from the balcony”) emphasizes the vantage point you’re observing from.
Both are grammatically correct; choose based on whether you stress being on it or looking from it.

Finnish verb endings show the subject. The -en in tarkkailen already means “I.”
Including minä is possible for emphasis (“Minä tarkkailen…”) but usually unnecessary.