The best place to start is by checking out Simple Talk, giving them your email address to get to download this book [Troubleshooting SQL Server: A Guide for the Accidental DBA](
https://www.simple-talk.com/books/sql-books/troubleshooting-sql-server-a-guide-for-the-accidental-dba/), or you can purchase it on Amazon.This book provides step by step advice along with the queries to find your pain points and how to troubleshoot them. It would also be very helpful for you to describe what your actual pain points are. "Performance Problems" is that with disk, CPU, network, memory, slow queries, query timeouts, etc? We would certainly need more information to provide a detailed response. So with a vague question, you get my vague response, however the book recommendation is awesome.