Firstly you can begin by understanding the relevance for the use of timestamp which is the detailed records on all transactions that has been performed and were recorded on the bitcoin blockchain network, all the above guides provided could give you more insight on that and it all depends on the needs and purpose at which you want to make the application, reading through the recommendations links will tell more.
Timestamps are used for validity and transparency.
Usually, timestamps become necessary when there is the need to prove a validation time of one transaction may be it due to financial transactions between two parties in which contracts or documents are involved. Another purpose indicated that it is to avoid double spending.
For miners, this is also used so that they can determine the difficulty of mining a block and adjust the parameters accordingly.