Learn Polish: Szłyśmy powoli wzdłuż tej ulicy. - We f were walking slowly along this street.

The verb iść has a very irregular past tense. While the masculine singular uses the stem szedł-, the feminine and non-masculine plural forms use the stem szł-. To say we were walking for a group of women, you take this szł- stem, add the plural ending -y, and finally attach the first-person plural ending -śmy to make szłyśmy.

If this was a mixed group of men and women, would the verb still be szłyśmy?

No. If there is at least one man in the group, Polish uses the masculine personal (often called virile) form. For this irregular verb, the stem softens to szl-, and you use the masculine plural ending -iśmy, resulting in szliśmy instead of szłyśmy.

Why does the sentence use tej ulicy instead of the basic form ta ulica?

The preposition wzdłuż (along) always requires the following noun to be in the Genitive case. Because of this, the basic phrase ta ulica (this street) must change to its Genitive feminine form, which is tej ulicy.

Why is there no word for we (my) in this sentence?

In Polish, the personal endings attached to past tense verbs, like the -śmy at the end of szłyśmy, already tell you exactly who is doing the action. Adding my is grammatically correct but usually unnecessary unless you want to add strong emphasis, like saying WE were walking, not them.