Не ешь это мясо: оно ещё сырое.

It is a negative command: don’t eat.

• ешь = the 2nd person singular imperative of есть (to eat)
• не ешь = don’t eat

This is the form you use when telling one person not to do something.

Не ешь is for one person in an informal situation.

If you were speaking to:

• more than one person, or
• one person politely,

you would say не ешьте.

So:

• Не ешь это мясо = to one person, informal
• Не ешьте это мясо = plural or polite

Есть is the normal, neutral verb meaning to eat.

Кушать also exists, but it is often:

• more colloquial,
• used with children,
• or used in polite invitations/offers.

In a plain warning like this, есть is the most natural choice.

Because мясо is a neuter noun.

The demonstrative this changes by gender:

• этот = masculine
• эта = feminine
• это = neuter

Since мясо is neuter, you need это:

• это мясо = this meat

Also, here мясо is a direct object, but because it is inanimate neuter, the accusative form looks the same as the nominative. So это still stays это.

Because мясо is grammatically neuter, so the pronoun referring back to it must also be neuter:

• мясо → оно

Russian pronouns agree with the noun’s grammatical gender, not with natural sex. In English we just say it, but in Russian that it can be:

• он for masculine nouns
• она for feminine nouns
• оно for neuter nouns

So оно ещё сырое means it is still raw.

In Russian, the verb to be is usually omitted in the present tense.

So Russian says:

• оно ещё сырое

Literally this looks like it still raw, but it means:

• it is still raw

This is completely normal Russian grammar.

Here ещё means still.

So:

• оно ещё сырое = it is still raw

This word can also mean other things in other contexts, such as more or another, but in this sentence the meaning is clearly still.

Сырое is the adjective сырой (raw) in the neuter singular form, agreeing with мясо.

Compare:

• сырой = masculine
• сырая = feminine
• сырое = neuter
• сырые = plural

Because мясо is neuter, the adjective must be neuter too:

• мясо сырое = the meat is raw

The colon introduces an explanation or reason.

So the structure is:

• Don’t eat this meat: it’s still raw.

The second part explains the first part.

You could also express the idea with потому что (because):

• Не ешь это мясо, потому что оно ещё сырое.

The colon version is shorter and very natural in writing.

Yes. Russian word order is fairly flexible, because grammar is shown a lot by endings rather than position.

The given sentence is a natural, neutral version:

• Не ешь это мясо: оно ещё сырое.

But you could also say:

• Это мясо не ешь: оно ещё сырое.

That puts more emphasis on this meat.

So the word order can move around somewhat, but the original version sounds very normal and natural.