As padmakar said, you can refer to HYSYS tutorial.
I will list down the steps anyway:
1. Enter HYSYS oil manager through simulation basis manager - oil environment button
2. Under "assay" tab (first tab) click on "add" button which will then open input data window for a new assay. Give a title to your assay at bottom field
3. For bulk properties, select "used" option and then fill all the data available on the right hand such as mol. wt., UOPK, visc etc
4. For assay data type, select "TBP" option which is generally available. Once you select TBP, a few more options will appear below and a table on the right side to enter assay % vs temp data. (you have to hit "edit assay" button to enter the vol% vs TBP data)
5. For light ends, select "input composition" which will then make a third bullet appear on right for light ends. Once you select this bullet, you can enter vol% of light components obtained from assay data
6. You can follow the same procedure for mol. wt, density and viscosity curve fields and enter whatever data is available with you in the assay.
7. Hit calculate.
8. Under oil charecterization window, go to the next tab of "blend". Hit add button. This will show you the available assay that you just calculated. Add this assay as a blend component and give the flowrate that you are going to work with (ex. 200000 bpd). Give a title to your blend and close the blend window which will take you back to oil charecterization window.
9. Go to the last tab of "install oil" which should show you the blend that you just created. Check the "ready" "install" boxes. type a name under "stream name" field like "Cold crude" which will then appear as a stream in your main simulation window.