Όταν το χαλί είναι βρεγμένο, γλιστράω εύκολα.

It basically means when, but in this sentence it has a whenever feeling.

Because both clauses are in the present tense, the sentence describes a general, repeated situation:

• Όταν το χαλί είναι βρεγμένο, γλιστράω εύκολα.
• Every time the carpet is wet, I slip easily.

So in natural English, when and whenever are both reasonable ways to understand it here.

Because βρεγμένο has to agree with το χαλί.

• χαλί is a neuter singular noun
• so the word describing it must also be neuter singular

The three basic forms are:

• βρεγμένος = masculine
• βρεγμένη = feminine
• βρεγμένο = neuter

Since the subject is το χαλί, Greek uses βρεγμένο.

It is a participle used like an adjective.

It comes from the verb βρέχω = to wet / to make wet or, depending on context, to rain.
The form βρεγμένος, βρεγμένη, βρεγμένο means wet.

So in this sentence, είναι βρεγμένο means is wet.

In practice, learners can usually treat βρεγμένο just like an adjective here.

Because το is the definite article, meaning the.

• το χαλί = the carpet / the rug

Greek uses articles very regularly, often more regularly than English does. In this sentence, the article works just as you would expect in English.

If you changed it to ένα χαλί, that would mean a carpet / a rug, which gives a different sense.

Because Greek often leaves subject pronouns out when the verb ending already shows the subject.

• γλιστράω already means I slip
• so εγώ is not necessary

You could say Εγώ γλιστράω εύκολα only if you wanted extra emphasis or contrast, for example:

• Εγώ γλιστράω εύκολα, αλλά εσύ όχι.
• I slip easily, but you don’t.

This is very normal in Greek.

Because the sentence describes a habitual or general situation.

• είναι = is
• γλιστράω = I slip

Together they mean something like:

• When the carpet is wet, I slip easily
• Whenever the carpet is wet, I slip easily

So this is not about one single event right now. It is about what usually happens in that situation.

γλιστράω means I slip or sometimes I slide, depending on context.

Yes, γλιστρώ is also used. These are two present-tense forms of the same verb:

• γλιστράω
• γλιστρώ

Both are acceptable in Modern Greek. A learner will often see both patterns with verbs of this type.

In this sentence, γλιστράω is the 1st person singular present form: I slip.

εύκολα is an adverb, meaning easily.

It modifies the verb:

• γλιστράω εύκολα = I slip easily

Compare:

• εύκολος / εύκολη / εύκολο = easy
  These are adjective forms and describe a noun.
• εύκολα = easily
  This is an adverb and describes how something happens.

So Greek uses εύκολα because it is describing how you slip.

Yes. Greek word order is more flexible than English.

This sentence could also be:

• Γλιστράω εύκολα όταν το χαλί είναι βρεγμένο.

That is also natural.

The version with Όταν first puts the condition first:

• When the carpet is wet, I slip easily.

So the original order is very normal, but it is not the only possible order.

The accent marks show which syllable is stressed.

In this sentence, the stress falls here:

• Όταν
• χαλί
• είναι
• βρεγμένο
• γλιστράω
• εύκολα

A rough pronunciation guide is:

• Όταν = O-tan
• το = to
• χαλί = kha-LI
• είναι = I-ne
• βρεγμένο = vregh-ME-no
• γλιστράω = ghlee-STRA-o
• εύκολα = EF-ko-la

A few useful sound notes:

• χ in χαλί is not English h. It is the rough sound heard in Scottish loch.
• ει in είναι sounds like ee.
• ευ in εύκολα sounds like ef before κ, which is why it starts EF-.