Muszę umyć ręce przed obiadem.

Because Polish often leaves out subject pronouns when the verb already shows who is doing the action. Muszę already means I must / I have to, so ja is not needed.

You can add ja for emphasis or contrast, for example if you mean I have to wash my hands, not someone else.

Muszę is the 1st person singular form of musieć, meaning to have to / must.

So muszę can be translated as:

• I must
• I have to
• sometimes I need to

In everyday Polish, it usually sounds like normal necessity, not always as strong or dramatic as English must can sound.

This is about aspect, which is very important in Polish.

• myć is imperfective: washing in general, repeatedly, or focusing on the process
• umyć is perfective: to wash something successfully, to completion

In Muszę umyć ręce, the idea is I need to get my hands washed before the meal, so Polish uses the perfective verb umyć.

Compare:

• Muszę umyć ręce = I need to wash my hands now / before that happens
• Muszę myć ręce przed obiadem = I have to wash my hands before dinner as a rule or habit

After muszę, Polish normally uses an infinitive.

So the structure is:

muszę + infinitive

Examples:

• Muszę iść = I have to go
• Muszę pracować = I have to work
• Muszę umyć ręce = I have to wash my hands

This is similar to English have to + verb.

Ręka is singular: hand / arm depending context.
Ręce is the plural form: hands.

In this sentence, plural makes sense because people normally wash both hands.

Also, ręce here is the accusative plural form, but for this noun it looks the same as the nominative plural. So:

• singular: ręka
• plural: ręce

Because with body parts, Polish often leaves possession unstated when it is obvious from context.

So Muszę umyć ręce naturally means I have to wash my hands, not someone else’s.

Adding moje is possible, but usually unnecessary and can sound emphatic:

• Muszę umyć moje ręce = I have to wash my hands

A very common alternative is:

• Muszę umyć sobie ręce

Here sobie helps show the hands are your own, but it is not required.

Because the preposition przed requires the instrumental case.

The noun obiad therefore changes form:

• basic form: obiad
• after przed: obiadem

So:

• przed obiadem = before dinner / before lunch

This is a case ending, not a different word.

It depends on context and on how the family or speaker uses meal words.

In Polish culture, obiad is usually the main cooked meal of the day, often eaten in the afternoon. In English, that may be translated as:

• lunch
• dinner

So both can be correct depending on the situation.

Because Polish does not have articles like English a/an and the.

Polish simply says:

• ręce
• obiad

The listener understands from context whether the meaning is definite or indefinite.

Yes. Polish word order is more flexible than English word order because case endings show grammatical relationships.

The original sentence is a neutral, natural order:

• Muszę umyć ręce przed obiadem.

But you can also say:

• Przed obiadem muszę umyć ręce.

This puts more emphasis on before dinner / before lunch.

Other orders are possible too, but some sound more marked or emphatic. The original version is a very normal default choice.