Complex sentence: It may be at the same level, at a higher level, or at a lower level than secondary education, anything from basic training to a Ph D. Higher education (also known as tertiary education) is education at a higher level than secondary education.
Split into simpler sentences: It may be at the same level, at a higher level, or at a lower level than secondary education, anything from basic training to a PhD. A form of this is higher education (also known as tertiary education), which is education at a higher level than secondary education.