Learn Hardcore Russian: Пожалуйста, говорите чуть громче.

Breakdown of Пожалуйста, говорите чуть громче.

What role does Пожалуйста play here? Is it the same as English please, and can it go at the end of the sentence?

Пожалуйста is a politeness marker, very close to English please.

In this sentence, Пожалуйста, говорите чуть громче. softens the request.
You can move it:
- Говорите, пожалуйста, чуть громче.
- Говорите чуть громче, пожалуйста.

All of these are natural; the meaning does not really change. Russian is flexible about the position of пожалуйста in polite requests.

Why is it говорите and not говори?

Both come from the verb говорить (to speak), but:

говорите is:
- the imperative for вы (you – plural or formal)
- also the present tense for вы (you speak / you are speaking)
говори is:
- the imperative for ты (you – singular, informal)

So:

Пожалуйста, говорите чуть громче. – polite/formal or to more than one person
Пожалуйста, говори чуть громче. – to one person you address as ты (friend, child, family member, etc.)

Is говорите here an imperative, or is it just present tense?