There are 4 important Portuguese contractions that you need to know. This is one of the hardest things for beginners to get the hang of. It took me years to feel confident using contractions. I think that if gender weren't involved they would be easy to pick up. That said, the contractions used in Portuguese are actually very intuitive and easy to pronounce.
***You think you have it bad? Learners of English need to wrap their heads around we'll, she'll, it'll, isn't hasn't wasn't wouldn't, shouldn't, and on and on.
Common Portuguese Contractions
Brazilians use these in everyday speech:
no & na : in the, on the, at the
em + o = no
em + a = na
In my head I would always think of the our "no". It took time before that eventually passed.
Notice that the no & na in these examples are expressing: in the.
Of course, there are PLURAL versions also. But let's keep it simple. You can get by just fine without the plurals until you are already making your own sentences. In most cases, you just add an "s" to get the plural anyway so no big deal! In this case, we have nos & nas.
num & numa : in a, on a, at a
em + um = num
em + uma = numa
do & da : of + the
de + o = do
de + a = da
ao & à : to the, at the
a + o = ao
a + a = à