Guernsey Post uses RoyalMail for the UK, parcels will be sent with a 'Certificate of posting' unless you specify 'Signed for' which will have a tracking number and insurance.
For International 'Royal Mail International Economy (Airmail)' will not include tracking or insurance, 'Royal Mail International Tracked (Airmail)' will.
Tracking will be available at www.royalmail.com if you have selected it.
Guernsey Post parcel costs are here www.guernseypost.com.