What is Amortisation of assets? How common is it?

[Good-Person]

There are many different kinds of assets that may prove to be really useful. However, maintaining the cost of such kind of asset could be very important as well. You must calculate the total expenses required to maintain the asset and its actual cost that may prove to be useful in the end. This means cost minus value of the asset might help us get a better picture of amortisation of assets. So, how is it calculated and why is it relevant?