Me lavo las manos.

Me is a reflexive pronoun. It shows that the action comes back to the subject:

• lavo = I wash
• me lavo = I wash myself

With body-care actions in Spanish, this reflexive structure is very common:

• Me lavo = I wash myself
• Me ducho = I shower
• Me cepillo los dientes = I brush my teeth

So in Me lavo las manos, me tells you that I am washing my own hands.

With body parts, Spanish usually uses the definite article (el, la, los, las) instead of a possessive like my or your, especially when the owner is already clear from the reflexive pronoun.

So Spanish prefers:

• Me lavo las manos = literally I wash myself the hands

But in natural English, we say:

• I wash my hands

The me already tells you whose hands they are, so mis is usually unnecessary here.

Because the verb has to match yo = I.

The infinitive is lavar = to wash.

Present tense of lavar:

• yo lavo = I wash
• tú lavas = you wash
• él/ella lava = he/she washes

So Me lavo las manos uses lavo because the subject is I.

It is basically lavar used reflexively.

• lavar = to wash
• lavarse = to wash oneself

You will often see Spanish dictionaries list both forms because both are common:

• Lavo el coche = I wash the car
• Me lavo las manos = I wash my hands / I wash myself

So lavarse is not a totally different verb in meaning, but it is a very common reflexive use of lavar.

Yes. That is grammatically correct.

Spanish often drops the subject pronoun because the verb ending already shows who the subject is:

• Me lavo las manos = natural
• Yo me lavo las manos = also correct

Adding yo can give extra emphasis, contrast, or clarity, for example:

• Yo me lavo las manos, pero él no.
  I wash my hands, but he doesn’t.

So in normal conversation, Me lavo las manos is usually enough.

It can often mean either one, depending on context.

Spanish present tense can express:

• a habitual action: I wash my hands
• a current action: I am washing my hands

So Me lavo las manos could mean:

• I wash my hands regularly
• I’m washing my hands right now

If you want to make the ongoing action extra clear, Spanish often uses:

• Me estoy lavando las manos = I am washing my hands

Both are possible, but the longer form emphasizes that the action is happening now.

Because with a conjugated verb, reflexive pronouns usually go before the verb:

• Me lavo las manos

But with an infinitive or gerund, they can attach to the end:

• Voy a lavarme las manos = I am going to wash my hands
• Estoy lavándome las manos = I am washing my hands

So in your sentence, me goes before lavo because lavo is a fully conjugated verb.

You could, and people would understand you, but it sounds less natural in this context.

For body parts, Spanish normally prefers:

• Me lavo las manos

Using mis manos may sound overly explicit unless you are contrasting them with someone else’s hands or emphasizing possession:

• Me lavo mis manos, no las tuyas.
  I wash my hands, not yours.

So the normal choice is las manos.

A very literal breakdown is:

• Me = myself / to myself
• lavo = I wash
• las manos = the hands

So literally it is something like:

• I wash myself the hands

That sounds strange in English, but it is a very normal Spanish structure for actions involving body parts.

Normal word order is:

• Me lavo las manos

Spanish does allow some flexibility, but unusual orders often sound marked, poetic, or emphatic.

For example:

• Las manos me lavo sounds unnatural in ordinary speech.

A more natural variation would be with emphasis or clarification in a larger sentence, but for basic everyday Spanish, stick with:

• Me lavo las manos

Then it would no longer be reflexive, because you are not washing your own hands.

You could say:

• Le lavo las manos = I wash his hands / I wash her hands / I wash their hands

Here:

• le tells you the action is done to someone else
• las manos still uses the definite article

So compare:

• Me lavo las manos = I wash my hands
• Le lavo las manos = I wash his/her hands

Yes. Me lavo las manos is standard and natural throughout Latin America.

The grammar is the same across the Spanish-speaking world:

• reflexive pronoun: me
• verb: lavo
• body part with article: las manos

So this is a very safe, widely used sentence to learn and use.