In manual testing, a tester manually verifies the functionality of the software. The tester has a comprehensive list of all the test cases they should test, along with the test data. They go through each case, one by one. They launch the software as an end-user would, enter the input, and manually verify the output.  

It may seem that manual testing is INEFFICIENT when compared to automated testing. It is slow, not REPEATABLE in a consistent manner, and prone to HUMAN misjudgment.

However, manual testing allows the tester to realistically test the software, using actual user data in a natural user environment, subject to similar external conditions. Only a human, not a computer, can evaluate the usability and ACCESSIBILITY of the application and how it looks and feels to the end-user. It also gives a broader perspective of the system. Finally, some test scenarios just can't be automated and NEED to be manually tested.

You should always test the software manually before trying to automate the testing.