The three basic types of policy are 'Third Party', 'Third Party, Fire and Theft' and 'Comprehensive'. The latter covers you for pretty much all eventualities, usually beyond an excess sum which you will have to pay yourself.
Most motorcycle cover is for replacement market value rather than an agreed value. So if your bike is written off in a crash, your insurer will get an assessor to work out the market value of your motorcycle prior to the accident. That’s what you’ll be paid, less your excess (some insurers will waive your excess if you are shown to not be at fault).
Third Party (TPO)
Third party insurance will cover any accidental damage you cause to other vehicles or property. Usually this is restricted to damage from a crash but some policies will cover other damage, such as that caused by things falling off your bike. Should you crash into another vehicle a TPO policy could pay the driver’s repair bills but it won’t cover damage to your bike at all. If your motorcycle isn’t worth much, it can be an economical form of insurance.
Third Party, Fire and Theft (TPFT)
As well as any damage to other people's vehicles or property, TPFT will cover your bike if it’s stolen or damaged by a fire. But you are still not covered for any damage to your motorcycle if you crash. If your bike is stolen and your insurer pays you its market value, it usually means they become the legal owner. So if it is found, it’s theirs to sell or dispose of as they see fit.
Comprehensive (Fully Comp.)
Comprehensive insurance includes the cover provided by TPFT and adds cover for damage to your own motorcycle. In the event of a write-off, you’ll usually be paid the bike’s market value less any excess. Fully Comp may also cover other costs involved after an accident, e.g. recovery, recovery and storage.
Some policies cover damage to things like your helmet and fixed accessories. You’ll need to check your policy, and if accessories are included you may need to inform your insurer of their fitment. Some accessories or modifications can invalidate your insurance, so make sure your insurer knows about them as part of your cover.