Nasal sounds, false friends, and every word inside a real sentence.
The two languages share a great deal of vocabulary, and a Spanish speaker can often read Portuguese without much trouble. Listening is another matter. Portuguese swallows unstressed vowels, runs words together and uses nasal sounds that Spanish does not have at all. Learners who arrive expecting an easy ride are usually surprised by how different it sounds.
That gap between reading and hearing is exactly why every word here comes attached to a full sentence. A word in isolation teaches you the spelling. A sentence starts teaching you the rhythm.
The tilde in "pão" and "amanhã" marks a nasal vowel — the air goes partly through the nose, and there is no separate n sound to pronounce afterwards. English has nothing quite like it, and neither does Spanish. Most learners get it wrong for a while, and everyone still understands them. It is worth practising, but not worth being paralysed by.
A note on "obrigado": it changes with the speaker, not the listener. A man says obrigado, a woman says obrigada, regardless of who they are thanking. It is a small thing that beginners get wrong daily.
The words in this game work in both. The real differences are in pronunciation, in some everyday vocabulary, and in how the two treat pronouns and the gerund. Brazilian Portuguese has far more speakers and far more media, so most learners hear it first — but the written language is close enough that learning one never wastes your time on the other.
Some words look like their English or Spanish cousins and are not. If you assume the meaning transfers, you will occasionally say something quite different from what you intended. The example sentences here are the cheapest way to catch that: seeing a word doing its actual job in a sentence beats trusting a resemblance.
Once a set feels easy, change the language you speak so Portuguese becomes the starting point. Producing a word is a different skill from recognising it, and that second direction is the one that matters when you are the one talking.