If you would like to create a custom button or link that will pass all the values to the New Shipment page so you don’t need to fill out any information then setup a button like this and replace the values you want:

https://rs-ship.na73.visual.force.com/apex/PrintPostageLabel
?relatedTo={!Orders__c.Id}
&relatedToField=Orders__c
&mailWeight=1.01
&reference=Ship Reference
&fullfilmentLocationId=a061I000001VzC2
&fromCompanyName=SleepPoint Diagnostics
&fromContactName=John Smith
&fromPhoneNumber=203-456-6309
&fromAddress=107 Mill Plain Road
&fromAddress2=
&fromCity=Danbury
&fromState=CT
&fromCountry=US
&fromPostalCode=06811
&toCompanyName={!Orders__c.Patient__c}
&toContactName={!Orders__c.Patient_Name__c}
&toPhoneNumber={!Orders__c.Patient_Phone__c}
&toAddress={!Orders__c.Shipping_Street__c}
&toAddress2=
&toCity={!Orders__c.Shipping_City__c}
&toState={!Orders__c.Shipping_State__c}
&toCountry={!Orders__c.Shipping_Country__c}
&toPostalCode={!Orders__c.Shipping_Zip_Code2__c}
&retURL=%2F{!Orders__c.Id}

Note that the available formats for fromState and toState parameters are state codes and state names, e.g. CA and California. For states consisting of two words, like North Carolina, you can pass the value as separate words or one word, e.g. North Carolina or NorthCarolina, and of course as a state code (NC). Also, letter case is not important, as you can pass the value in all possible combinations, like NORTHCAROLINA, northcarolinaNORTHcarolina, etc. Same with state codes.