some questions about doing exchange

Hi there, stupid questions ahead... could someone please explain to me how studying abroad works? Im about to start an exercise science degree at USYD and would really love to go on exchange in Sem 2 2027, specifically at Peking University. I'm a little lost with all the information that's out there so need some help understanding what I need to prepare in order to maximise my chance of going overseas.

By 'saving up electives', does this mean that for Sem 2, 2027, it's best if I only have one/two units selected (ie. my core units required for course completion) and have the rest of them saved up as space to study at the exchange university? How do I complete the unit offered by USYD while the exchange university?

On the study abroad website, it says that 24 usyd credit points = 15 from the host uni. Does this mean I should have an entire semester with no usyd units at all???

Those who have done exchange abroad - how did you go about planning for your semester exchange and selecting your units?

Thanks!