When using the verb "do" to ask a question, the tense inflection is on "do" and the main verb is in it's infinitive (base) form.
For exmple, as a statement, you would say "Your friend goes shopping" but when you make it a question with "do" it is "Does your friend go shopping?" "Does" is in present tense third person singular form, and "go" is uninflected. Below are more examples of this:
Use "does" for present tense third person singular. Use "do" for present tense first and second person singular and plural, and third person plural. Use "did" for past tense of all persons and numbers.
I hope this helps.