Is it easy to get admission into Oxford university, harvard University,
'Easy' depends on what your profile has been. Top universities like Harvard and Oxford look for motivated students who have been performing well in their previous degrees also.
They also look for students who have good extracurriculars.
For undergraduate admissions, Harvard accepts SAT scores. You should have very good scores to be accepted by Harvard.
Along with the SAT, your application will have a number of questions which will help them evaluate you on a number of areas. These count too.
Finally, what your referees say about you will also be taken into consideration.
Do revert for more information.
All the best.
And if any exam you have given yet?