First i need to know why we use environments under pipelines in Azure devops and Is there any Monthly/Yearly limitation in creating build or releases in Azure DevOps? Anyone Please HELP !
Here is a doc about the advantages of using environments.
1.Deployment history
2.Traceability of commits and work items
3.Diagnose resource health
4.Permissions
whether there exist any limit on the number of builds that can be made
There is no limit. You can create hundreds or even thousands of pipelines for no charge. You can register any number of self-hosted agents for no charge.
But as you said, they have build time limit and parallel job limit.
You could refer this doc for more detailed information.