In our project, we are creating users instead of contacts in Sitecore to track users interaction. For that, we need to log in that user in Sitecore first. Can we create contacts instead of users in Sitecore 7.2?
Sitecore contacts were introduced in 7.5 together with xDb.
Before Sitecore 7.5 it was Sitecore DMS and Sitecore OMS.
Many people were not happy with Sitecore DMS.
I suggest you to upgrade to new releases of Sitecore (releases 8+) rather than try to implement on Sitecore 7.2.
Mainstream Support of Sitecore 7.2 ended in Dec 2017 and you have one more reason to upgrade to new releases.