Practice, practice, practice. Theory is not everything. You need to apply what you learn from reading. These exercises will help you improve your “integration skills” by putting into practice what you’ve leant here https://addjustabitofpi.com/integration-techniques-integration-by-parts/ about integration by parts. If you don’t remember the basic integrals and their rules, click on these two links: https://addjustabitofpi.com/2019/10/03/fundamental-integrals/ https://addjustabitofpi.com/2019/10/03/rules-and-properties-of-integrals/. Check your results here: https://addjustabitofpi.com/2019/10/09/integration-by-parts-solution-with-procedure/.