As I said before, the data is uploaded using LSMW, Winshuttle, Data Sync manager, etc.
For LSMW or for other tools as well, create data in spreadsheets (saved as *.TXT files).
Go through each LSMW step to create an object for each transaction (e.g.,PA40 for pers.action, PA30 for empl data maintenance).
Links are given below (instead of my copying the same here). You can find lot of good stuff if you care or take the trouble to search with google.
Developing an Effective Strategy for HCM Data Conversion (PA, OM, BN) | Symphony Consulting Blog
Creating OM and PA data thru LSMW | Symphony Consulting Blog
LSMW for Functional Consultants in simple step-by-step way
Steps to create a simple LSMW using batch input recording - ABAP Development - SCN Wiki
LSMW- BATCH INPUT RECORDING - YouTube
**************** - LSMW using Recording
**************** - LSMW Tutorials
SAP HR | Easy Upload, Download to Excel | Winshuttle Software