Eu aqueço a água para o chá no fogão.

Aqueço is the 1st person singular (eu) of the irregular verb aquecer (“to heat”). Present indicative:

• eu aqueço
• tu aqueces
• ele/ela aquece
• nós aquecemos
• vós aqueceis
• eles/elas aquecem

Note the spelling change: c → ç before -o to keep the /s/ sound.

In Portuguese, c before e or i sounds like /s/, but before a, o or u it would normally sound like /k/. The cedilla (ç) forces the /s/ sound before o:

• aqueço = /aˈse.su/
  Without the cedilla you’d get an incorrect /k/ sound.

Portuguese often uses definite articles before nouns, even when English omits them. Here you’re referring to a specific water you’re heating, so you keep a:

• Eu aqueço a água = “I heat the water.”
  If you drop the article, it sounds ungrammatical in Portuguese: Eu aqueço água isn’t standard.

The acute accent marks the stressed syllable and indicates a hiatus (two separate vowel sounds) in á‑gua:

• Stress falls on the first syllable (Á‑gua)
• Without the accent, you might accidentally form a diphthong or misplace the stress
  Portuguese orthography uses accents to guide both stress and vowel separation.

Para is a preposition meaning “for” or “in order to.” Para o chá = “for the tea.” In Portuguese you normally keep the definite article:

• Correct: para o chá
• Omitting it (para chá) sounds odd unless you rephrase, e.g. para fazer chá (“to make tea”), where chá stays without an article.

No = em + o, meaning “in/on the.” You need the definite article o before fogão:

• em o fogão → no fogão
  Simply saying em fogão is ungrammatical; the article is required.

Yes. Esquentar is a common synonym meaning “to warm/heat up.” You could say:

• Eu esquento a água para o chá no fogão.
  Subtle nuance:
• aquecer often implies heating to a higher or more precise temperature
• esquentar is more general (“to make warm”)