On a higher level, you need to:
a. Create Native Styles (native ad templates) in Google Ad Manager.
b. Create Native Ad Units (steps are quite similar to that of regular banners, but under sizes, you need to add “Fluid or Fixed” for native ads units).
c. Create Line Items and Add Creatives (based on the campaign – guaranteed or non-guaranteed).
If you need complete step-by-step help, refer our Google Ad Manager native Ads guide.