Sunburns of the skin are a first degree burn and rarely are serious enough to require medical treatment.
Most sunburns which are only first degree burns are painful but usually the sunburn goes away on it's own within a few weeks to a month depending on how badly you're sunburned.
The more sunburned you are the longer it will take to get rid of the sunburn and sometimes but rarely sunburns may require medical treatment at a clinic.
You can apply some Aloe Vera Gel to the sunburn and even butter to the sunburn which can help ease the pain and help the sunburn heal.
Applying some ice in an plastic bag to the sunburn can also help.
Also soaking in a cool bath will help the pain of the sunburn go away and ease the pain.
Taking aspirin can help manage the pain of the sunburn as well.
When out in the sun to prevent sunburn make sure to wear shirts that are not easily seen through and keep your back covered as well as arms when possible.