What can you do with tracking codes in Salesforce?

3 custom fields

Wherever you want to track, create the following 3 fields:

CASE(  
text(Shipping_Provider__c),  
'UPS', 'http://wwwapps.ups.com/WebTracking/track?track=yes&trackNums=' + Tracking_Number__c ,  
'FedEx', 'http://www.fedex.com/Tracking?action=track&tracknumbers=' + Tracking_Number__c,  
'US Postal Service', 'https://tools.usps.com/go/TrackConfirmAction_input?qtc_tLabels1=' + Tracking_Number__c,  
"")

Note for Lightning Experience Users

"Hey, that works on classic, but not Lightning!"

Right, there's a change in how links are generated. When Classic sees you returning a string that looks like a link, it displays it as a link.

In Lightning, use the hyperlink formula:
HYPERLINK(url, friendly_name [,target])

CASE(  
text(Shipping_Provider__c),  
'UPS', hyperlink('http://wwwapps.ups.com/WebTracking/track?track=yes&trackNums=' + Tracking_Number__c, "View") ,  
'FedEx', hyperlink('http://www.fedex.com/Tracking?action=track&tracknumbers=' + Tracking_Number__c, "View"),  
'US Postal Service', hyperlink('https://tools.usps.com/go/TrackConfirmAction_input?qtc_tLabels1=' + Tracking_Number__c, "View"),  
"")

As an added bonus, you'll get your friendly text instead of a nasty long URL.

LEX Shipping Link