Manual Testing is the type of testing that is performed manually by humans. It is time-consuming as well as takes numerous human resources. You can use it to perform explanatory testing. The investment in this testing is lower as compared to Automation Testing. In the long run, its rate of return is comparatively lower. Due to the possibility of errors by humans, it might not be completely accurate.
Automation Testing, on the other hand, uses automation tools in order to execute test cases. It is significantly faster when compared with Manual Testing. It does not allow random testing. Even though the initial investment is high in this type of testing, it has a better rate of return in the longer run. It is extremely reliable and performed using scripts and tools.
If you wish to make a career in Automation Testing then register for Test Architect Certification.
Also, watch this video on the difference between Manual and Automation Testing: