Πότισε το φυτό λιγάκι.

Here it is being used as a command: Water the plant a little.

But this is a very good question, because πότισε can also be the 3rd person singular aorist form meaning he/she/it watered. In an isolated written sentence, Greek can sometimes be ambiguous like that. Normally, context and intonation make it clear.

So:

• Πότισε το φυτό λιγάκι. = Water the plant a little.
• In another context, the same words could mean He watered the plant a little.

Πότισε is the 2nd person singular aorist imperative active of ποτίζω (to water).

That means:

• 2nd person singular = you are talking to one person
• imperative = it is a command / instruction
• aorist = it presents the action as one complete action

So Πότισε is the kind of form you use when telling one person to do something once, as a single act.

Because Greek normally uses the definite article with a specific noun much more regularly than English does.

So το φυτό means the plant:

• το = the for a neuter singular noun
• φυτό = plant

In Greek, leaving out the article often changes the feel or meaning, so το φυτό is the normal way to say the plant here.

It is in the accusative case, because it is the direct object of the verb Πότισε.

You are telling someone to water the plant, so the plant receives the action.

A detail that often confuses learners: with neuter singular nouns, the nominative and accusative are often the same in form. So:

• nominative: το φυτό
• accusative: το φυτό

The form does not change here, but the function in the sentence does.

Λιγάκι means a little, a little bit, or just a bit.

It is very close to λίγο, but λιγάκι often sounds:

• a bit softer
• a bit more colloquial
• sometimes slightly more gentle or friendly

So:

• λίγο = a little
• λιγάκι = a little bit / just a little

In a command, λιγάκι can make the instruction sound less blunt.

That word order is very natural in Greek:

• Πότισε = verb
• το φυτό = object
• λιγάκι = adverbial word meaning a little

Greek word order is more flexible than English, so you can move things around for emphasis. For example:

• Πότισε το φυτό λιγάκι.
• Πότισε λιγάκι το φυτό.

Both are possible, but they may sound slightly different in emphasis. The original order is straightforward and natural.

This is an important Greek aspect difference.

• Πότισε = aorist imperative
  Focuses on one complete action
• Πότιζε = imperfective imperative
  Focuses more on ongoing, repeated, or process-like action

So:

• Πότισε το φυτό. = Water the plant.
  One act, one instruction
• Πότιζε το φυτό. = Keep watering the plant / Water the plant regularly / Be watering the plant
  Depending on context

In this sentence, Πότισε fits the idea of giving a simple one-time instruction.

By itself, it is a normal imperative, so it is fairly direct. That is not necessarily rude in Greek; it depends on the situation.

It can sound perfectly natural:

• between family members
• between friends
• in practical instructions
• when speaking to a child

Also, λιγάκι softens it a bit.

If you wanted to make it more polite, you could say something like:

• Πότισε το φυτό λιγάκι, σε παρακαλώ. = Water the plant a little, please.
• Μπορείς να ποτίσεις το φυτό λιγάκι; = Can you water the plant a little?

A rough pronunciation guide is:

• Πότισε = PO-ti-se
• το = to
• φυτό = fi-TO
• λιγάκι = li-GHA-ki

The stress falls on:

• Πότισε
• φυτό
• λιγάκι

A slightly more accurate pronunciation is:

• Πότισε = /ˈpotise/
• το = /to/
• φυτό = /fiˈto/
• λιγάκι = /liˈɣaci/

Two useful sound notes:

• φ sounds like English f
• γ in λιγάκι is not a hard English g; it is a softer Greek sound

In Modern Greek, stress marks are normally written on words of more than one syllable, so they show you where the word stress goes:

• Πότισε
• φυτό
• λιγάκι

This is very helpful for learners, because stress is important in Greek pronunciation. The little accent mark tells you which syllable to stress. So the written sentence is already giving you pronunciation help.