Mash-ups for Employee Central

We are using Employee Central along with On-premise Payroll. For data replication, we are using HCI. We would like to use the Mash-ups in Employee Central to publish Payslip and other standard functionalities available. I searched for relevant documentation and unfortunately could not find right document. Though many documents are available, each document mentions different step for using Mash-ups.

Can Experts pleas help me with 1) please explain what's mash-up and I can use this and 2) Please share relevant document or the link for such document which would help me to successfully complete the configuration and start using mash-ups.

Thanks & Regards

S. Chandrasekaran