Tengo que pagar la multa hoy en el banco.

Yes. Tener que + infinitive is a very common way to express obligation in Spanish, equivalent to have to in English.

• Tengo = I have (from tener)
• que = introduces the obligation
• pagar = infinitive (to pay) So Tengo que pagar = I have to pay.

Tener is the infinitive (to have). In a real sentence you usually conjugate the verb to match the subject.

• yo tengo = I have
  Spanish often drops yo because tengo already shows it’s I.

No. This que is not the question word qué (what).

• que (no accent) is used in structures like tener que (to have to)
• qué (with accent) is what, used in questions/exclamations: ¿Qué pasa? (What’s happening?)

Yes, and the meaning is very similar:

• Tengo que pagar... = very common, neutral, everyday obligation
• Debo pagar... = also means I must/should pay, can sound a bit more formal or “duty-like” In Latin America, tengo que is extremely common in conversation.

Multa means a fine (for example, a traffic fine or penalty fee). It’s a feminine noun, so it takes feminine articles:

• la multa = the fine Spanish normally uses the definite article (el/la) more often than English does in this kind of sentence.

Yes, hoy (today) is flexible. All of these are natural:

• Tengo que pagar la multa hoy en el banco.
• Hoy tengo que pagar la multa en el banco.
• Tengo que pagar hoy la multa en el banco. (less common, but possible) Changing placement can slightly shift emphasis, but the basic meaning stays the same.

Because en expresses location: at/in the bank (where the payment happens).

• en el banco = at the bank
• al banco = to the bank (movement/destination), from a + el = al If you want to emphasize going there, you’d use a verb of motion:
• Tengo que ir al banco a pagar la multa. = I have to go to the bank to pay the fine.

In Latin American Spanish:

• banco = bank (financial institution)
• banqueta = sidewalk (common in Mexico and some other areas)
• banca can mean bench or banking sector depending on context, but for a physical bank building you want banco.

Pagar is usually used as:

• pagar + [thing]: pagar la multa (pay the fine) You use a mainly when you mention the person/entity receiving the money:
• pagarle al banco / pagar al banco (pay the bank) But in your sentence, the focus is the bill/fine itself (la multa), so no a is needed.

Because banco is a masculine noun, so it uses the masculine article:

• el banco = the bank
  lo is not used as the. Lo is usually a neuter article/pronoun used in other structures (like lo bueno, I like it = me gusta eso/lo depending on context), not for naming regular nouns.

You can, but it’s optional:

• Tengo que pagar... is the most natural and common.
• Yo tengo que pagar... adds emphasis or contrast (like I have to pay, not someone else).