Interviews are by appointment only. When National Visa Center completes their processing (usually within a few weeks), they will forward your case file to the U.S. Embassy Riga. The Consular Section will send you a notification inviting to prepare for a visa interview upon receipt of the case file in Riga.
K visa applicants should proceed as described here: Instructions for K visa applicants (PDF-119 KB).
Applicants are requested to strictly follow the above instruction and schedule their visa interviews only after receiving a notification from the U.S. Embassy Riga and obtaining the required documents.