Hello! - ¡Hola!
Have a good day! - ¡Qué pase/s un buen día! (Tú/Usted)
How are you? - ¿Cómo estás (tú)?, ¿Cómo está usted? 

In English there is only a singular second-person form of the personal pronoun, but in Spanish, when we talk to another person, we can say “tú” (is less formal) and “usted” (more formal: for people that you do not know or with whom you want to express a special respect, formal letters, etc.).

In consequence, in plural you can say “vosotros” or “ustedes”.

Thank you - Gracias.
What’s your name? - ¿Cómo te llamas?, ¿Cómo se llama (usted)? 

My name is Carmen. - Me llamo Carmen. 

I am Carmen - ¡(Yo) Soy Carmen! 
And you? - ¿Y tú? ¿Y usted?

In English (and other languages as, Deutsch, Dutch, French...), saying the subject in a phrase is compulsory. In Spanish, you can say the subject if you want, but it is not compulsory. In these cases, the subject is understood.

In Spanish, when we make a question, we must write the interrogation and exclamation points at the beginning and at the end of the phrase.

Pleased to meet you! - ¡Encantado/a de conocerte/le! (Tú/Usted).

We end the adjective “encantado/a” in “o” or “a” depending on the genre of the person who is talking. We say “encantado” if the subject is masculine and “encantada” if it is feminine.

Please - Por favor
Thank you - Gracias 
You're welcome - De nada
Excuse me - Disculpa/e, perdona/e (Tú/Usted)
(I'm) Sorry - Lo siento
Goodbye - ¡Adiós!
See you later! - ¡Hasta luego!
I don’t speak English/Spanish (well) - No hablo ingles/español (bien).
Do you speak Spanish - ¿Habla/s español? (Usted/Tú)
Is there someone here who speaks English/Spanish? - ¿Hay alguien aquí que hable ingles/español?

In English we can say “there is” or “there are” depending on if the subject is singular or plural, but in Spanish there is the unique form “hay”, and it does not matter the number of the subject. Example: Hay una persona. Hay cinco personas. Hay muchas personas.

Help! - ¡Socorro! ¡Ayuda!
Good morning - Buenos días
Good afternoon / Good evening - Buenas tardes

In Spanish we say “Buenas tardes” from 12 o’clock midday untill 9 or 10 p.m., when we say “Buenas noches”, but the hour is not exact. And this can change a lot between winter and summer, as in this case there are more light hours.

Good night - Buenas noches
I don't understand - No entiendo/comprendo.
I don’t understand you – No te/le entiendo/comprendo. (Tú/Usted).