Learn Turkish: Bir sorum var. - I have a question.

Turkish doesn't have a direct verb for "to have." Instead, you use a structure that means "my [thing] exists." Here, sorum means "my question" and var means "exists" or "there is." So literally, the sentence says "A my-question exists."

How does the word soru change to sorum?

The base word for "question" is soru. To say "my question," you need to add a possessive suffix. Because soru already ends in a vowel, you just add -m instead of a longer suffix like -im or -um.

Does bir mean "one" or "a" in this sentence?

It serves as both! In Turkish, bir is the number one, but it is also used as the indefinite article for "a" or "an". Here, it translates naturally to "a question."

Why does the word var come at the end?

Turkish sentences generally put the main action or state of being at the very end. Since var provides the core meaning here (telling us that the question "exists"), it takes the final spot in the sentence.