Difference between High level testing and Low level testing:-

High Level Test Cases:- These test cases define the functionality of a software/product in a broader way without going into deep functionality. Like if we have to write high level test cases for login functionality we'll test that 'User should be able to login success full with valid credentials'.
Advantages :-Its advantage is that a tester is not bound to follow the test cases step by step and thus it gives a chance to explore more edge cases. This also increases the chance to find new bugs.
Disadvantages:- Its disadvantage is that its not sure that all scenarios are covered and its difficult for an inexperienced tester to work with these test cases.
 

Low Level Test cases:- In software testing these test cases define the functionality of a software/product in deep way. These test cases generally include details like 'Excepted Result', 'Test Data',etc. Like if we have to write low level test case for login functionality then we'll describe UI of the login page(user name & password text boxes, Save, Forget password link), URL of the login page, login with proper test data(valid credentials).
Advantages:-Its advantages is that a tester is unlikely to miss bugs and also its easy for an inexperienced tester to work with these test cases as he can easily get the desired results by following steps.
Disadvantages:- Its a tedious to executes these test cases again and again and tester may not find job challenges.