What is the purpose of Schedule B on Form 990-PF?

Schedule B is used to provide information about any contributions received by the foundation during the taxable year. Any foundation filing the Form 990-PF must attach a Schedule B if,  the foundation directly or indirectly received contributions valued $5,000 or more in the form of cash, non-cash, or any other securities during a tax year.
 
XYZ is a private foundation and has received contributions of $8000 in cash during 2019 through various sources. So while filing the Form 990-PF for 2019, XYZ has to attach a Schedule B along with its Form 990-PF to explain the contributions.
 
Any foundation that is not required to attach a Schedule B along with the Form 990-PF, must make sure to check the box on Line 2 in Part I of the Form 990-PF.