"The pants have pockets."
Translation:As calças têm bolsos.
As a verb, it would take on a verb form and be the word, "Calçar" which only conjugates to "Calças" when using the familiar "tu" 2nd Person form of you.
Calçar as a verb usually means to "put on" and usually refers mostly to shoes (especially for say, horses) and some sources say gloves, but not pants which would likely use, "vestir" instead to put on, and wear (which can also take "usar" especially in Brazil).
Calçar is also related to paving, as in the sidewalks (Calçada) that the Portuguese are famous for having:
So it is also somehow related to "treading" which is related to feet and shoes.
To shoe, to pave, to shim, to tread, to underlay...
Spelled as you have without the cedilla on the "c" the word would be pronounced, cal-ka(s).
Calças as a noun for pants also is only feminine, and also plural so it would be, at best, "Eu calço as calças" (at least in the other Portuguese speaking countries).
Not as sure how Brazilians wear their pant(s). :)
Refer to this for more information:
It's the difference between 3rd person singular (he, she, it) and 3rd person plural (they).
- ele/ela tem
- eles/elas têm
Since the noun «as calças» is plural, you need to choose the corresponding plural verb conjugation «têm».