Can I use o-levels to enter a university in the US?

No, O Levels (Ordinary Levels) are not directly accepted for university admission in the US. US universities require either a high school diploma or its equivalent (like the International Baccalaureate or A Levels). O Levels are considered a secondary school qualification, but they aren't equivalent to a complete US high school education. You would need to demonstrate the equivalent of a US high school education through other means to be eligible for US university admission.