The following are based on the documentation at the Mountain West Digital Library.

Once you navigate to the appropriate URL, you may have to right-click the page and View Page Source to see the XML.

Identify

Identifies the OAI provider:
http://digitalcollections.uark.edu/oai/oai.php?verb=Identify

List sets

Lists all the collections (sets) on your server:
http://digitalcollections.uark.edu/oai/oai.php?verb=ListSets

List metadata formats

Lists all the metadata formats on your server. The format "oai_dc" is required of all OAI providers.
http://digitalcollections.uark.edu/oai/oai.php?verb=ListMetadataFormats

List identifiers

Gives the header information only for all records (starts with first group of headers, in this case 200):
http://digitalcollections.uark.edu/oai/oai.php?verb=ListIdentifiers&metadataPrefix=oai_qdc

For the next group of headers, use the "resumptionToken" value at the end of the results:
http://digitalcollections.uark.edu/oai/oai.php?verb=ListIdentifiers&resumptionToken=Cyrus:56:oclc-cdm-allsets:0000-00-00:9999-99-99:oai_qdc

List records

List the records from one collection, in this case "BAD Times":
http://digitalcollections.uark.edu/oai/oai.php?verb=ListRecords&metadataPrefix=oai_qdc&set=BADTimes

Change the collection name to get another set.  Use the collection "nickname," for example, "Cyrus." 

Lists the records from all collections (first group of records, in this case the first 1000):
http://digitalcollections.uark.edu/oai/oai.php?verb=ListRecords&metadataPrefix=oai_qdc

For the next group of records, insert the "resumptionToken" value from the end of the results:
http://digitalcollections.uark.edu/oai/oai.php?verb=ListRecords&resumptionToken=Cyrus:56:oclc-cdm-allsets:0000-00-00:9999-99-99:oai_qdc

Get record

Get a particular record (e.g., item #3092 in the Ozark Folksong Collection):
http://digitalcollections.uark.edu/oai/oai.php?verb=GetRecord&identifier=oai:digitalcollections.uark.edu:OzarkFolkSong/3092&metadataPrefix=oai_qdc

Tips

Metadata queries include deleted records, which will show up as brief entires, "deleted."  Don't panic if you see these.

More Information

See The Open Archives Initiative Protocol for Metadata Harvesting section on Protocol Messages.