Learning Portuguese grammar is probably the second most important thing to learn after vocabulary in order to achieve communicative proficiency and then fluency.
In order to comprehend the majority of spoken language, it is essential to master the following key concepts:
- Focus on the present tense of regular -ar, -er, and -ir verbs
- Learn the grammar construction Estar a + infinitive / Estar + gerundio to describe actions in progress
- Become familiar with the distinction between the imperfect and the preterite (past) tenses
- Learn the simple future and ir+infinitivo to talk about the future
- Understand when and how to use definite and indefinite articles
- Learn pronouns (demonstratives, possesives, relatives etc.)
- Understand how to use the passive voice
- Get familiar with the use-cases for subjunctive mood (especially in the present tense)
And remember, grammar is important, but even more important is the continual expansion of your vocabulary so that you can understand and be understood.