That would be a very long post, but in a nutshell medals generally fall into various categories: medals for service, medals for active campaign service, decorations for gallantry, MBE’s etc.
To give you a simple example, here’s my collection:
From left to right:
Campaign medal for Operation Telic : 30 days continual service in Iraq during the 2003-2009 Iraq conflict
Operational Service medal for Afghanistan: 30 days service in Afghanistan
Operational Service medal for Iraq and Syria: 30 days service in the operation against ISIS, with clasp for service in Iraq or Syria
Queens Diamond and Platinum Jubilee medals: 5 years service in the day of each jubilee
RAF Long Service and Good Conduct medal: 15 years service without any serious disciplinary issues
You can find out about every medal that can be awarded here:
Details of the medals awarded to serving members of the armed forces, veterans and MOD employees; and who can receive them.
www.gov.uk
…and understand why holders of the Victoria or George cross are held in such high regard.