The main purpose for condoms is prevent pregnancy and inhibit the spread of STDs (Sexually Transmitted Deceases).
Beside that, condoms are often used to protect toys. Some femdoms also use condoms for humiliation purposes. Here the male subject is made to wear several ticker (usually low cost bulk) condoms so that he does not feel much when penetrating his mistress. The erection of the male is often maintained with a cock ring or medication.

Most condoms are made of latex and can therefore not be used with oil based lubricants. Oil based lubricants can break down latex, making it easier to tear and will also deteriorate the material quickly so that they will no longer protect against pregnancy and STDs even though they will look good to the eye. Use water based lubricants instead. Also, make sure to apply the lubrication after the condom is in place to avoid getting unnecessary lube on the inside of the condom.
If the condom is used to cover a toy, for anal sex or any other use where pregnancy and STDs are not a consideration, oil based lubes should still be avoided since the oil can cause the condom to easily break.