If you speak Portuguese, some English grammar rules will feel natural and others will feel confusing. These are the biggest differences to focus on first.
Portuguese and English both use SVO order, which helps a lot. The main difference is that Portuguese allows more flexible word order — subjects and objects can sometimes be moved. English word order is strict.
Portuguese has four articles (o, a, os, as) that change based on the noun's gender and number. English has no gender system — just 'the', 'a', and 'an'.
Portuguese has the personal infinitive — a unique verb form where the infinitive itself changes ending depending on who is doing the action. English has no equivalent concept at all.