Although we do not print "stamps" per se., we do have first class postage that is printed on a label with your Ship To and Ship from address on it.
The same as a stamp - but with a printed address label.
You do have the option of printing directly on a envelope, or on a sticky label, or you can print the label
on regular paper and tape / glue it on. Sticky labels does make it easier but are not required.
Here are samples of different sizes of postage labels and how they would look.